Rainwater Harvesting Help

I've been planning for the past few weeks to upgrade our rainwater harvesting and storage system for irrigation purposes - we live in Orange NSW and the drought is really starting to make it hard to keep our veggie garden going.

Currently all downpipes on our house are plumbed to a single drainage trench in our backyard, I'd like to collect solely from our garage roof (independent structure to house) and utilise a wet system design to store in 2x 4000L tanks, from there it would be connected to a pump which supplies a single tap for hose connection, and a manifold and sprinkler system for automated garden watering.

I'm a DIY enthusiast and plan to do most of the work myself, with sign off/final inspection from certified tradespeople. I plan to hire a trench digger for running all piping so I should get a pretty consistent grade along the drop for all pipes.

My garage roof is 9x5m=45m2 collection area, and I plan on installing a new downpipe for the system (and closing off the previous downpipe) on the south-west corner of the building. The eave height above ground level at this point is 3m and I understand I should install my leaf and mosquito screening at this point. I would then trench down to tank-1 in the southern corner of my yard (taking care not to interfere with the waste line running parallel).

The underground run from down pipe to tank 1 is approximately 14m, and I have measured fall as 1" over 2' - meaning a total fall of around 13cm over the length of the run. I plan to install a sediment trap per viewtopic.php?p=1193459#p1193459 - https://forum.homeone.com.au/viewtopic.php?f=35&t=92701&p=1844675#pImg977558 as well as low restriction inlet to tank 1.

These are the tanks that I'm planning to use - https://www.bushmantanks.com.au/product/4000-litre-domed-squat-rainwater-tank/ - this is dictated by the largest size that I can get through the garage for installation.

I'm currently planning to take overflow from the 2nd tank and dig a new drainage trench in my yard - run it to an agi-pipe with sock buried in the ground surrounded by gravel and geomesh fabric. My pump would also be connected to tank2 approx 150mm from the bottom of the tank, and use a floating pickup tube on the inside to take water from around 200mm below the surface layer.

Summary

• System purpose: vegetable irrigation only, non-potable use however will likely provide drinking water fill up for chickens
• 2x 4000L tanks -- should I connect in series, or parallel? - https://www.bushmantanks.com.au/product/4000-litre-domed-squat-rainwater-tank/ - https://www.bushmantanks.com.au/wp-content/uploads/2019/06/TXD910-Tank-Drawing-NSW.pdf
• Tank Inlet height 1300mm (bottom of strainer); tank height 1457mm
• Catchment area of 45m2 - postcode 2800
• Single downpipe (can add an extra one if it helps) with gutter sole height of 3000mm
• Wet line run of approx 14000mm with drop 1":2' -- I assume 100mm DWV pipe?
• DIY sediment trap and DIY waterbouy
• Low restriction inlet to water tank

Please let me know your thoughts on my system and help me with some further indication of what calculations I need to make, and sizing for my piping.

Yard diagram showing existing house waste collect (lines with measurements close to house) and sewer line (red line along the western boundary) is shown below. Coloured sections are my planned irrigation zones (my veggie patches). Diagram is north oriented.


Thank you so much for taking the time to read my thread.

I have prepared a system diagram based on SaveH2O 's sediment trap diagram

You have a very good understanding of rainwater harvesting best practice. I'm impressed!

I looked at the long term average annual rainfall which is about 930 mm/yr.

Yield (with no first flush diverter) is usually about 85% due to evaporation etc. If you started having annual rainfalls of 500mm (a huge drop), the garage roof could be expected to produce 19,125 L annually but what the future will bring, only Elon Musk knows. Have you worked out roughly how much water you think you will need at certain times of the year and whether those times are usually wet or dry?

If you went back to an average rainfall year, your harvest would be about 35,570 L annually.

Have you thought about diverting water from 2 or more downpipes to aid you during dry periods?

The sediment trap is installed in a non turbulent section of pipe, usually at least 4 metres past the last point of turbulence such as an elbow or tee. Settled sediment is mostly stationary on the bottom of the pipe due to water flowing in boundary layers but when it moves, it simply drops into the 'trap' and later flushed. It works well.

The low restriction inlet sweetens the tank's bottom anaerobic zone with oxygen rich water and because it has less density than the settled (higher density) water on the bottom of the tank, it quickly de-energises and flows upwards.

The ICON leaf diverter is better than others on the market but I don't know whether it is still sold. Bunnings had it for $38 but they no longer advertise it. The others are not good.

This sounds like a lot of work.

The tank's pump supply valve doesn't have to be high off the tank's floor when fitted with a floating inlet hose. +150mm of water above the pump's supply valve can't be accessed because a typically sized pump will generate a free surface vortex that will draw air into the pump which can cause the pump's pressure controller to register low pressure and switch the pump off. Ingesting air is also not good for the pump. Critical submergence is the term used for the distance between the outlet and the water surface and the distance depends on the discharge flow rate and the outlet size.

If the valve is 150mm above the bottom of the tank and there is another +150mm of unusable water above that, that is a high % of unusable water in a tank that only has 1.3 m depth to the overflow's invert.

An irrigation outlet will usually make a floating inlet hose for you (usually about $70) but make sure that it has a compatible fitting with the other side of the valve. It is often best to have the manufacturer fit it. It is also a good idea (if possible) to have a stainless collar/ring around the filter at the top of the hose to keep the filter above the bottom of the tank when the water level is low.

Re the tanks, it states that they are 4,200 L but also states 4,000 L elsewhere. Most tanks state a size that doesn't include the storage space lost after fitting the overflow, that is, if you delete the overflow outlet, you will increase the tank's capacity and the % increase is particularly handy when it is a squat tank.

If the planned tank overflow plumbing is not ideal and you like the idea of increasing the tank's capacity by eliminating the overflow pipe plus the vertical riser as well as retaining the downpipe as is, have a look at the Supadiverta. It is a syphonic (drainage) downpipe diverter with an internal 750 micron filter and when height adjusted to a downpipe, the tank only fills to a predetermined height via a low restriction inlet. You can also either permanently or remotely harvest additional downpipes when needed.
https://www.supadiverta.com.au/

Thank you very much, your posts on the forum have been extremely helpful in planning my harvesting system.


This question sent me down a rabbit-hole of comparing rainfall data from BOM. Based on what I've discovered it's always wet and always dry




We are enthusiastic gardeners and love to grow as many vegetables as we can. We generally will be growing some sort of vegetables all throughout the year so our water requirements don't vary too often. Certainly through Summer the water demand would be higher due to the heat, and throughout Winter we generally would be growing vegetables with lower water requirements.

It looks like April and October are certainly our driest times of year which means we'd need to manage our water carefully through end of Summer, and hope for wet Winters to collect for the seasons ahead.

I certainly appreciate planning off lower than average rainfalls as I feel using conservative figures in calculations yields more appreciable results in real life application


For clarification, are you referring to harvesting from additional downpipes on the same catchment area, or additional downpipes on the house roof?

The south corner of our house roof does slightly overhang the garage roof, and it would be possible to route rainwater from the gutter onto the garage roof catchment area. However I'm unsure of how to calculate the capacity of the guttering and proposed downpipe to handle this additional flow.

If the latter, harvesting direct from another downpipe, this would be possible but likely involve a fair amount of work in order to do a 'neat' looking job - a concrete path surrounds our house so running any additonal piping down to the tanking or a common collection point would require either exposing pipes, tunneling under paths, or destroying/recreating the concrete path.


Thanks for this information, based on this I believe it would be a good idea for my to change my water path from the original plan of inputting to Tank-1; and instead input directly to Tank-2 as I'll be able to lay straighter pipes and induce less turbulence in the water path whilst maintaining a 4m gap from the tank input.

Is there any requirement for a minimum distance from the sediment trap TO the tank input?


Of course! Thanks for that, totally overlooked that fact.

Can you please elaborate on this point. Do you just mean like a stainless steel pipe clamp to hold the filter to the hose, or a more substantial device to provide some 'spacing' for it to rest on if the tank water gets low? I am planning to use an OpenSprinklerPi system for irrigation control, so can easily program a low tank level sensor to ensure no pumping is done at insufficient water volumes. This may negate the need for the collar if it is for that purpose?

Great observation - the detailed drawing also states 4,150L which is a 3rd figure to throw in the mix. I'll speak with the manufacturer and find out the exact details and confirm deletion of overflow is possible (or whether I would just need to cap it) and whether they can install the floating pickup etc.


Having read through the Supadiverta website and watched the video a few times now I certainly believe it would be an ideal solution in my system application.

Would you recommend in my system configuring the tanks in series or parallel? My reading on the topic leads me to believe that for my purposes (irrigation) a parallel configuration (wherein the tanks are balanced and fill evenly) would be ideal, and that the series configuration is more so for drinking water purposes as it allows more comprehensive removal of suspended particulate matter through a 'settling tank' arrangement.

Thank you again for your valuable input in my system design and the others you've helped on the forums over the years.

It annoys me when I see sites advising people who are considering tanks to use climatic averages and online calculators to work out how big their tanks need to be. We cannot predict variability that occurs at all times of the year and the best protection is to maximise the amount of water collected during unexpected dry periods when most needed. This obviously doesn't apply to households off the water grid who need to collect every drop but for your situation, it is the best path to follow.

I think that using a Supadiverta is your best choice but option it with the bigger 25mm vertical drops which includes purgers.

By height adjusting the Supadiverta to the downpipe so that excess water is diverted back down the downpipe when the tanks are full, you eliminate the need for a tank overflow, you can cap the overflow outlets to increase the tanks capacities, you won't have a vertical riser, the pipes are smaller and stronger, the water is filtered plus you can plumb the horizontal pipe so that you can remotely link 18mm garden hose or 19mm poly pipe to a second Supadiverta during rain in times of need.

Re draining an additional roof area to the garage roof, I have understood that there is one downpipe on the garage. Eaves gutter/roof area/downpipe compliance is calculated by your regions 1:20 Average Recurrence Interval which is based on an average rainfall intensity over a 5 minute period. You are in a 150 mm/hr ARI region which is an average rainfall intensity of 2.5 mm/min over the 5 minute average duration. This means that during a 1:20 ARI, your 45 sq m garage roof would drain a minimum 112.5 L/min. Your downpipe and the Supadiverta can handle more volume than this but you should divert only partial additional drainage. It is a good idea.

No. Suspended sediment settles as bed load reasonably quickly and 4 metres if practicable of straight length past the previous elbow or tee is fine. All that ends up in the tank is a small amount of very fine suspended sediment. It is a totally different type of sediment layer if you could even call it that, it is more like a thin layer of talcum powder. An added bonus is that the water left in the smaller wet system pipe is the cleanest water that came off the roof during the last rain event whereas water retained in a standard wet system is invariably rank.

Another bonus of the sediment trap is that little water is wasted when flushing and it can be collected anyway.

The latter. It is something that few floating inlets have. It can't be too heavy though but more important for a standard harvesting system with the usual sediment layer. For garden watering and for a system with multiple best practice safeguards, you really don't need it.

I would have the valve that supplies the pump optioned about 70-80mm above the the bottom of the tank at the valve's lowest point but note that they measure the valve height from the central point. The two balance lines and the low restriction inlet's height can be the same.

The low restriction inlet's size depends on the length of the run but it would most probably be 40mm. The internal diameter (ID) of class 12 pvc pressure pipe is 42.8mm but cheaper Class 9 is 44.1 ID a 6.2% volume increase that equates to roughly a 9% potential higher flow rate.. The class ratings are pressure ratings.


It should be a 90mm outlet, Bunnings sell a cap that fits inside it for about $2.20. Just lightly smear some Silastic around it.


Most tank manufacturers don't allow for the volume lost with the overflow fitted when stating tank capacity but your tank's manufacturer apparently has which is unusual but commendable. I guesstimate that fitting a 90mm overflow to your tank would decrease capacity by about 340 L (each tank) from the overflow's invert to the top of the wall.

I always consider the overflow's height to be the height of the pipe's invert because that is what determines the tank's storage capacity unless there is a raised section of overflow pipe inside the tank. Just clarify with them whether they measure from the invert or the central point as they would a valve.

Water needs to breathe but laying some shade cloth on the tank's top meshed inlet will block the sun.

A settling tank system is ideal even when using a Supadiverta and a sediment trap. It rarely costs more to do it best so why not? The tanks need to be linked anyway.

As a matter of interest, several years ago I bought a Total Disolved Solids (TDS) meter to measure the water delivered to my pump. I first tested my tap water (Melbourne's water is a very high standard) which was 29 mg/L from memory and so I thought that I would do the ridiculous and measure the water in my wet system next. It was 16 mg/L!!! I mentioned it in a Homeone post several years ago.

https://www.melbournewater.com.au/water ... er-quality

Water is traditionally diverted to the top of the tank where it falls down and resuspends the sediment and taken from the bottom of the tank where the worst quality water is when everyone should be diverting to the bottom and taking the better quality water from near the top.

Sorry I don't see the option I need to pick on the SupaDiverta site for this - can you please PM me, or post here, the exact product configuration options for my application?


So as long as I keep the bottom of the filter screen in the Supadiverta at an absolute height lower than the lowest point of the mesh screen on the tank(s) overflow will be achieved back to the downpipe, I could also route the middle (lowest of the 3) outlet of the Supadiverta back into the downpipe, or along the same path for the 'first flush'.

The only existing downpipe on the garage roof is over part of the concrete path which would make running the two charged harvesting lines of the diverter to the tanks difficult - ie. either need to chase the concrete path, or expose the pipework. Hence I'd most likely prefer the option to install a new downpipe on the southern end of the garage which would allow me to trench the pipework down to the tank siting quite easily. Overflow management of course becomes more of a difficulty but I'm happy to go with my original plan to dig a new drainage trench -- shouldn't be too hard if I'm hiring a trencher anyway, just need to cut a few trenches side-by-side then connect them with a shovel.


I'm not sure what you mean by plumbing the horizontal pipe sorry - do you mean taking water off from the 'capture' pipework prior to it arriving at the tanks? Interesting concept.

No vertical riser certainly appeals to me - easier to manage insect and debris ingress in that configuration. So the 'low restriction' inlet near the bottom of the tank would be the only feed-in mechanism on the tank system correct?


I'll grab a photo of the current configuration of downpipes this afternoon. If I keep the existing downpipes connected on the main house roof then I imagine the additional catchment 'overflow' from the roof to garage would be minimal but not negligible in the long term - a good outcome indeed.


I believe by moving my proposed downpipe to the southernmost corner of the garage and infeeding directly to tank-2 I'll actually be able to run a straight path all the way along the charged line(s) which would be excellent for the water turbulence.

A quick question that this raises for me - would I be better to do two runs of 25mm piping down to the tank(s) and combine at the inlet, or combine at the beginning of the horizontal run and a larger diameter piping the whole way?


In reply to my email they haven't really stated if the overflow is included in the calculation...




Yes very odd that this is the norm in rainwater tank setups. I've seen some of your 'horror' posts on other threads on HomeOne - it's amazing the lack of work some 'professionals' get away with...

A range of optional outlet fittings are included free of charge but the 25mm option with purger is currently shown at a compensatory low price under the "valve socket reducing" heading. It needs updating but I currently include them at no additional cost to customers who should have them.

Yes.

There is a website address on both sides that is the same height as the top of the internal reservoir wall that also locates the bottom of the filter. You can use this as a line of sight with a long straight edge and spirit level.

When the tanks are full, water will also be retained in the Supadiverta and if this is drained, then a corresponding height (95mm) of water in the tanks will backflow to the Supadiverta and also drain.

The middle flush outlet is set lower than the bottom of the reservoir floor and any grit etc that settles on the reservoir floor and moves over the outlet is captured during the entire rain event.

If you don't have the optional first flush kit that manually drains and you don't need it for garden watering anyway, then either a 20mm pressure pipe or 19mm poly pipe fitted with an inline valve on a horizontal section of pipe is used. A pvc or poly inline tap (valve) should not be used on a vertical pipe because when the valve is closed, fine sediment will sit on the turning mechanism which will often damage and/or jam it.

Re first flush diverters, if you see a Homeone member's photo of their water tank, you will invariably see a substandard installation and one of the most ridiculous fails is when a first flush diverter is fitted to the top of a vertical riser. The installers just don't understand that the first flush will fill with the settled water in the riser while the actual first flush is in the downpipe at the other end of wet system! I have also seen numerous hydraulic engineer's drawings that show this and then they don't fit a flap valve to prevent mosquitoes from accessing the standing water. Every day is Be Kind To Mosquitoes Day for these guys.



Have a look at the installation above. None of the pipework needs to be there.

• The nearest downpipe is diverted to an underground sump that rises to an unshielded opening above the tank.
• The sump will build up crud and there is no way to clean it.

• The two copper pipes and the power outlet indicate a submersible pump is in the tank yet the vertical riser discharges water directly above it which is great for resuspending sediment in the pump's immediate vicinity.
• The useless first flush is tiny in any case and would hold no more than 4 litres, the probable amount that the dripper is wastefully discharging to the stormwater pipe every hour.
• The overflow pipe severely restricts the already narrow space between the tank and the fence.
• Overflow outlet reduces the tank's volumetric capacity.
• The ugly step sister.

Gutters slope towards a low point where downpipes are fitted. You will need to do some flow tests and probably alter the slope.

I would need to see photos to comment.

If you plumb a tee or a wye to the Supadiverta/tank supply pipe, you then have several options that allow you to fit an inline valve and a sprinkler adaptor that can connect to an 18mm hose. A similar arrangement would also be on the second Supadiverta and all you do is connect the hose between the two and open the valves.

The photo below shows a reducing tee.


People also use a similar option to have a reduced size riser coming up from below ground and attaching to (usually) a 90 degree faucet elbow (female thread at one end. This usually attaches to a 3/4" male threaded x 19mm barbed inline tap that uses 19mm poly pipe to gravity feed drip hoses. The tee(s) is/are positioned at convenient positions along the larger supply pipe and it negates having to connect gravity fed lines to a tank.



Yes.

I recommend connecting the supply pipe to the tank's valve by using a short length of UV stabilised flexible hose fitted with a pvc hose tail at the pipe end and a poly nut and tail at the tank end. The nut and tail allows the hose to be easily removed if ever needed.



A rule of thumb to follow is that is you double a pipes *(true) diameter, you increase the volume x4 but if you have the same hydraulic head, you increase the flow rate by nearly x6 due to the reduced friction loss. Class 12 pressure pipe 25mm (29.8mm ID) and 40mm (42.8mm ID) internal volumes are 0.7 and 1.44 litres per metre respectively.
*Pvc pressure pipe sizes are nominal.

The two vertical drops usually merge to a larger pipe below the Supadiverta to reduce friction losses. A 25mm 90 degree elbow and a 40x25x25mm tee (see below) are often used but there are several options.

Because the syphonic outlets are at different internal heights, two pipes are often plumbed separately so that the lower internal outlet has prioritised flow to, for example, a tank or a drip hose and when the tank fills or the rain intensity increases and the water in the reservoir rises, the water then diverts down the higher outlet to a second tank etc.

For a longish run, there is also the option of connecting the 40mm pressure pipe to cheaper 50 mm DWV pipe and fittings. The IDs are 42.8 and 51.6mm respectively. All fittings are BSP and tapered poly reducing nipples are used for the connection.

You are probably the first person to have ever ask them but they appear to be saying that the tank expands by 150 litres when full. That is a heck of a lot and I find it hard to believe. 150 litres?

I'll send you a PM with screenshot just to make sure I'm ordering the right part. Thanks.


What a dogs breakfast of an installation, I feel sorry for the owner. Unfortunately seems like a lot of this kind of thing happens in newer builds - shameful.


No worries, will jump up on the ladder this weekend and get some work done!

Will provide some photos for context this week.


Thanks I understand what you're saying now - basically a gravity fed line direct from the tank infeed (before reaching tank(s)) rather than a pumped line. I don't think I'll bother with this as it probably won't be required for my application.


This seems like a great solution to me. So I'll have 2x 25mm 3m (to sole of gutter, real life will be minus a bit of downpipe and minus the supadiverta) drop into the reducer (expander?) and my 40mm run with sediment trap at least 4m after the start of the run.


Checking the pricing difference I don't think there is much saving for me to make by switching to the larger pipe, especially at the 'risk' of the thinner wall section incase anything ever happened the pipe.

Yeah a little bit excessive in my view also. I imagine the extra storage was more likely a capped intake screen during testing rather than expansion of the body.


I've changed my design slightly as I realised I could actually get a slightly larger tank through the access in my garage. I've gone ahead and ordered 2x 5000L tanks from TankWorld - https://www.tankworld.com.au/tanks-accessories-pumps/5000l-round-corrugated-deal/ - and additionally decided to site them side by side rather than with one opposite the other. This should make it easier to run the intake line as I'll only need to cross over my house waste line once instead of twice - much lower risk profile.

Water in a riser pipe will be the same level as in the tank. You can use this for other uses apart from connecting to a low riser to supply suitable drip hoses away from the tank, for example, you can connect a riser to a gravity fed tap either above the pipe or away from the pipe and tank.

There are several valve options at the end of the pipework but it is obviously best to have an outlet that is comfortably low and as useable as possible, for example, having space for a watering can.

You only need to include a reducing tee in the pipework with the tee's branch either vertical or horizontal when you want to make a branch line. A reducing tee would usually not be used on a long branch line, the pipe's diameter would be reduced at the end of the branch run near the tap.

There are several pressure pipe fittings that have male and female bsp threads and there are usually several options available for intended usage.


Yes.

It's called a reducing tee although you would use it to increase the pipe size.

To eliminate the tank's overflow pipe and plumbing, you need to be careful when judging the levels when the tank is some distance away. Do you know someone with a laser level? A plasterer or carpenter perhaps. A small laser level with a limited distance could be used with a midway reference point...someone holding an upright stick for example. You can hire them but hiring a professional use one (the only ones that I have ever seen for hire) is more expensive than buying a small one.

https://www.bunnings.com.au/bosch-pll-1 ... r_p5660477


Good price!

I don't recommend very high overflow outlets unless the overflow is modified inside the tank with a bellmouth but it matters not in this instance. The photo below shows a very large tank with a low overflow outlet which allows for a high flow bellmouth plumbed above the outlet. For a high positioned overflow outlet, the internal pipe needs to be a U.

For residential use, high positioned overflow outlets are not good because the tank has virtually no mitigation during heavy rain when the tank is full. Horizontal draining pipes are less efficient than standing vertical pipes and the mosquito proof overflow mesh which usually has an open area of less than 55% also presents a flow restriction.



The fittings at the garage end are few and all that is required with the pipes are couplings.


It is best to use a flexible UV stabilised pond hose or similar to connect the pipe to the tank.

AT PIPE: You need one faucet socket (female bsp thread at one end) and a pvc hose tail.


TANK END:
One poly M + F elbow (elbows are neater because they can be angled downwards).
One poly nipple.
One poly nut and tail.

As always SaveH2O, excellent advice!

Stewie

I'll certainly ask around but my current plan was a bit of old school physics. Use a clear hose with water in it and set one end at the height of the tank top, then use the water level at the other end to set the height for the SupaDiverta.

I've done a bit of digging (literally) and planning over the past week, have determined that I'll be able to use my existing downpipe on the garage, as well as one that captures from the main house roof and the carport rooftop - my extremely helpful neighbour is going to help me cut out some concrete in the footpath to run the pipework then fill it back in.

I've included some photos below which will help give context on the downpipe locations.










What are your thoughts on the middle outlet for my installation given the context of pipe locations? One approach would be that I could fit the 'optional first flush kit' shown on AquaTrek site and run the drainage line of it straight into the exiting downpipe pipework underground.

Per https://www.supadiverta.com.au/first-flush-kit.html I could take the outflow from the 19mm tap (k) to a 19mm barb drilled straight into the side of the elbow joins in the underground drainage section (drill a hole in the elbow, thread in a 19mm director and silastic around the outside) - the first flush would be manually drained after longer dry periods by opening the 19mm tap.

What are your thoughts around combing the flow from both downpipes to the tank inlet? I'm assuming I'd likely need to move to 100mm DWV pipe to cope with the larger flow rate.

My tanks have been optioned such that the primary feed tank will have a 40mm inlet approx 150mm up from the bottom of the tank, it will overflow through its top 90mm outlet into a 100mm inlet (they don't do 90 for some reason) on the secondary tank (also approx 150mm from bottom up). Finally the pump will be attached via a 25mm outlet (150mm up) which will come out into an elbow, then a straight run into the pump itself (at a length of at least 250mm to prevent cavitation of the pump). I'll also have some shutoff valves at every appropriate point.

If you retain the garage downpipe, you only need to empty the flush into the downpipe.

If you fit another downpipe elsewhere and then block the current garage downpipe, you can drain the flush anywhere. Unlike first flush diverters that have a wasteful dripper, ones that manually drain capture a set amount of water that is but a small % of the water lost by common flush/dripper systems.

For vegetable garden watering, you don't need a first flush diverter fitted, there already is an internal 750 micron filter that ejects solid bird droppings and dead insects etc. The alternative is to fit a 19mm poly pipe or a 20mm PVC presssure pipe to the middle flush outlet that will capture a tiny amount of dirty roof wash but continually capture any heavier sediment that falls to the reservoir floor throughout the entire rain event. This also gives you the option to leave it open for the first 5-10 minutes of rainfall after a dry period.


If you divert the existing downpipes, you will have to drain to the tank's top inlet and have a standard wet system. You will also need an overflow pipe on the tank.

You have to remember that when tanks are filled by a standard system, water continues to be diverted into the tank even when the tanks are already full, an unnecessary quirk that is now seeing countless tanks (and swimming pools) in NSW and Vic full of orange water and a layer of red silt at the bottom as the result of rain falling during a time of concentrated atmospheric dust.


It looks like the two gutters supply a 100x75mm downpipe.

I think that your idea of diverting some of the water from the house gutter to the garage gutter is a good one and the simplest solution.


Fitting the 25mm pump draw valve 150mm above the bottom of the tank is too high, 80-100mm is more than ok when using the Supadiverta system and a settling tank. Those tens of mm represent a lot of unusable water.

The 40mm inlet valve can be a little higher than the 25mm valve because the pump's pressure controller will cut the pump off when it detects low pressure and this happens when the pump starts drawing a free surface vortex. This happens before the water level drops to the top of the 25mm valve. 150mm is ok if they measure the valve from the mid point as nearly all do.


You need to have two 32mm balance valves fitted about 100mm above the bottom of each tank .

If you overflow through the top 90mm overflow, you will always have one tank full...you may as well just buy one tank!

A 100mm bottom inlet (balance) valve on the second tank is absolutely unnecessary in this case. I super, super strongly recommend dumping this idea.

You have to remember that when the settling tank fills, the water diverted to that tank will match the amount of water flowing through the balance line. The tank will not overflow if the Supadiverta is correctly height adjusted.

All you need to do is divert a 40mm pipe to a 40mm inlet on the settling tank. No cutting up concrete paths, no diverting 100mm pipes to a tank's top inlet, no overflow pipes needed and certainly no leaving one tank full of water.

I so basically a mixture of the two plans would be sufficient -- if I fit 3x 25mm drops from the supadiverta, and at the bottom of the middle one place a gate valve. The middle one beyond the gate valve would drain directly into the underground junction of the existing downpipes. After a few min of rain after a dry spell I could open the valve and flush that initial first wash.




Sorry I'm not sure I understand why this is. I think you may have misinterpreted what I was asking...
Quote myself:What are your thoughts around combing the flow from both downpipes to the tank inlet? I'm assuming I'd likely need to move to 100mm DWV pipe to cope with the larger flow rate.

What I meant was combing the flow from the captured downpipes from the SupaDiverta... so the 2x 2x 25mm vertical drops. Originally we discussed 2x 25mm = a 40mm horizontal run. What I'm now enquiring about is collecting using two Supadivertas, my assuming is 100mm pipe would be best suited for the horizontal.



Roger that, will follow up with manufacturer.


My understanding with placing the tanks in series for settling was that you'd want to overflow from the top of the first settling tank into the secondary tank where the pump draws from? Are you suggesting instead to balance them at a much lower level? I thought this more reflected a parallel type setup.

Example diagram (don't laugh at my drawing skills) of the system with the series setup as I've outlined.

If the optional first flush kit isn't used, the middle flush outlet is invariably still used to capture sediment and the option is there to drain it anywhere at any time and duration but possibly/probably most are diverted to the downpipe.

Most use a 20mm PVC pressure pipe but using 19mm poly pipe allows a variety of simple connections to the downpipe. PVC pressure pipe is neater though.

To plumb a 20mm pressure pipe to the downpipe, it needs to pass around the adjacent vertical drop and it also needs an inline tap/valve fitted to a horizontal section of pipe.

The best 20mm PVC fittings to use (in order from the valve socket) are:

1. One 20mm 45 degree elbow.
2. One 20mm 90 degree faucet elbow (female BSP 3/4" thread at one end).
3. One 3/4" BSPM x 19mm barbed inline valve.
4. One19mm poly elbow.

The poly elbow fits into a 22mm hole drilled into the downpipe. 22mm hole saws are used for electrical glands and you may know someone in the trade.

The length of the flush vertical drop is determined by the length of the 20mm pressure pipe between the valve socket and the 45 degree elbow.


I included the standard size tennis ball in the photo to show the area of the internal flow path to stormwater.
The filter is set at 50 degrees.


The fittings are shown above plus 2 x 20mm pressure pipe sleeves and a short 19mm poly pipe to join the valve and the poly elbow.



Yes, the references to combining the flow from two downpipes to a 100mm pipe diverted to the tank's inlet threw me. I read it several times as well. Ok, that is now cleared up.

The second large downpipe collects from two roof areas but I don't know their combined area. This needs to be known but you are better off diverting water from the house gutter to the garage gutter. The vertical drops can drop a few hundred mm and run along the wall before a second vertical drop. Until they reach ground level, they must remain either vertical or horizontal as sloping the pipe will break the prime at that point.


If harvesting two downpipes, the pipe and 40mm low restriction inlet needs to be upgraded to 50mm.

When you buy pressure pipe, it is cheaper per metre in 6 metre lengths and irrigation outlets are usually cheaper than the big green shed.

Because the head varies with the height of water in the tank, the low restriction inlet will have higher flow potential when the tank water is low. This is another reason why you don't want an overflow from the top, the inflow to that tank will be limited when the tank is almost full yet the second tank could be nearly empty.

A parallel system usually entails having a manifold arrangement that distributes water to each tank, it is not a settling system. Some customers have a floating inlet hose on the first tank's balance valve and this works well. It is also my recommendation. If you also fit a sediment trap, the water will be very clean and the water retained in the smaller wet system pipe will be the best quality water that fell last when it rained.

Noted thank you - to keep it 'clean' looking I'll likely do a vertical drop the same as the other two ports, and drain into the downpipe line underground that I've excavated. When I backfill the hole I'll be planning to put an irrigation valve cover/box in to allow for future access. Most likely I'll put a solenoid on the line and wire it into the irrigation controller so I can setup automatic rules for draining the line after x minutes of rain, or manually do it with the push of a button


The carport roof is 29m2 of which 100% is collected to the single downpipe. The main roof is total 157m2, of which 45m2 is on the downpipe side -- I'll double check the fall on the gutters tonight to see what is actually captured by this downpipe.


Makes sense, thanks for the helpful diagram.

That makes a lot of sense. I've emailed the tank supplier and asked them to change the 100mm inlet to a 32mm inlet, and add an additional 32mm outlet on the other tank such that I can setup the balance line. Hopefully I'll also be able to install the floating pickup hose for it.

Hopefully I can come up with some arrangement to harvest from the second downpipe, otherwise half the work I did on the weekend was for nothing

It is really interesting that you mention fitting a solenoid and an irrigation controller to the first flush line. When I first researched all facets of rainwater harvesting, I determined that an ideal first flush system would be solenoid controlled to automatically dump the collected water rather than have a wasteful and high maintenance archaic dripper system. The problem I encountered was that the solenoids needed a minimum 20 kPa to operate and so I abandoned the idea but maybe there is a suitable product now.

During that research phase, I came across a website called Frank's Workshop which amazingly enough was based in Melbourne. He also did some research on suitable solenoid valves, you might find it interesting reading.

http://www.franksworkshop.com.au/GWS/Phase1/Phase1.htm (scroll down)

He went into a lot of detail about solenoids etc but when I tried to buy the valve he used, it was no longer available.

I still have a new unused Holman Dial Ezy irrigation controller with all instructions that I was going to use in my short lived solenoid research, you are welcome to it if it would be of any use to you.

I also have a brand new unused Irritrol 3/4" solenoid here that is just taking up space, you are quite welcome to have that as well if you have a use for it.

You will notice that he also looked at some rainwater diverters. I won't comment except to say (which he never) that if the downpipe's flow path is obstructed, the products are not compliant when fitted. There still are several such products for sale at major hardware outlets and plumbers still willingly fit them! You will find several different non compliant such products in the big green shed. The big green shed also sold large numbers of the two discussed by Frank.

The downpipe that merges the two roof areas is 100x75mm. This can be adapted to the Supadiverta 100x50mm inlet by using a 100x80x90mm and a 95x45x90mm downpipe adaptor. A metal 100x75 downpipe can also be cut and folded to fit the inlet's internal dimensions which are 107mm x 57mm. A suitable sleeve (or 3) could also be made from the section of downpipe removed.

The larger downpipe obviously drains a large combined roof area and it would be good if some of that water was sent to the garage roof to more evenly distribute the volume of water sent to each Supadiverta during heavy rain.

Draining a large combined roof area through several Supadivertas is never a problem (and still not need a tank overflow pipe) but maximising harvesting yield during light rainfall is more important than sizing pipework to cope with heavy rain when the tank(s) would quickly fill anyway. It is also important to occasionally flush the stormwater system and this is automatically done when the tanks are full.

An irrigation shop can usually make one for you but it would have to be fitted to the tank's bulkhead fitting so it is collectively installed at the same time. Maybe the tank supplier can make one for you but make sure they use a food grade hose and not one that will host bio film.


If you upsize to 50mm pipe, you would plumb a 40mm pipe from the second Supadiverta and connect it to a 50x40mm reducing tee in the line going to the tank.

We try to use 45 degree wyes for greater efficiency when connecting to an existing pipe but 50mm wyes are very expensive. Even the 40mm wyes are fairly expensive but to encourage their use, I sell them at cost to help customers. I don't stock 50mm wyes but I could get one included in a shipment and sell at cost if you wanted one.

The extra fitting has to be fitted just past the first Supadiverta because there is no room between the two 25mm vertical drops for another fitting.

LATE NOTE: Make sure that the tank valves you option are in their best positions.

Also, have you thought about getting power to the pump?

I didn't even think of that part of the problem. I've done a little bit of googling and found some discussion around low pressure solenoid valves here - https://forum.arduino.cc/index.php?topic=238723.0 - apparently 'direct lift' is the terminology used to describe them. Brass body on most of them too which should be fine with rain water acidity. Hopefully I'll be able to find one that is 24VAC, otherwise I'll just have to drive it via a relay with 12VDC if required.

Nice one thanks - I'll have a read through it today.


That's very kind of you, but I'm happy to leave that to someone who is more in-need of it. The OpenSprinkler board I'm getting has more than enough zones for my needs, I'd happily take the solenoid off your hands though

I'll double check the fall on all the gutters this afternoon, if my thoughts around it are correct then I should be able to achieve that with minimal work required.


I'll reach out and see if they can, or indeed if they can fit if I supply it prior to manufacturing.


Sounds good - so I'll have:
SD1 - Captures from most of main roof and carport
- 2x 25mm drops combined into a reducer to 40mm line


SD2 - Captures from part of main roof and all of garage roof
- 2x 25mm drops combined into a reducer to 40mm line

Then combine the 2x 40mm lines into a single 50mm line which goes to the tank input via DIY sediment trap.

Will the 50mm line be sufficient for the flow rate required or is friction loss too high?


The current order is
Tank1 (primary fill/inlet tank)
- 40mm inlet at 10 o clock
- 32mm inlet/outlet for balance line at 9 o clock

Tank2
- 32mm inlet/outlet for balance line at 3 o clock
- 25mm outlet to tank at 9 o clock

Do I need to ask if I can increase the size of the 40mm inlet at 10 (supply line) or will it not really matter if i adapt down the supply line at this point due to friction losses etc. by the time it reaches the tanks.



Thanks for checking, I bet a lot of people overlook this! I'm digging an additional trench from garage to shed (where pump will live) at 600mm deep to lay conduit for my sparky to wire up to a enclosure/distribution box in the shed. I'll be getting them to add a new circuit for this purpose and also terminating an additional powerpoint in the garage --- why not!

Aussie supplier for low pressure solenoid - https://core-electronics.com.au/brass-liquid-solenoid-valve-12v-1-2-npt.html - https://core-electronics.com.au/plastic-water-solenoid-valve-12v-1-2-nominal.html

It's yours. It's just gathering dust here. It has a straight flow through design.

Yes.

I have been calling this SD 2 but SD1 it now is.


Yes.

The 40x25x25mm tee has a seamless transition from 25mm to 40mm whereas to go from 25mm to 50mm would mean having a 50x25mm reducing tee at the 25mm vertical drop which would require a 50x25mm reducing bush at one end of the run. It is best not to have the change of elevation at the pipe run that this would entail. The 40mm pipe would then connect to a 50mm tee via a 50x40mm reducing bush to pick up the 40mm pipe from SD1.

Just check the line that the 40mm pipe from SD1 will take to the 50mm tee. It is best to use two 45 degree elbows instead of two 90 degree elbows.


If you double a pipes internal diameter, you increase the volume x4 but if you use the same head, you increase the flow rate nearly x6. This tells us that there is a flow rate increase nearly 50% greater than the volumetric increase.

Class 12 25mm pressure pipe holds 0.7 litres per metre. (23.7mm ID)
Class 12 40mm pressure pipe holds 1.44 litres per metre.(42.8mm ID)
Class 12 50mm pressure pipe holds 2.265 litres per litre. (53.7mm ID)

50mm pvc pressure pipe has 3 times less kPa friction loss per metre than 40mm pvc pressure pipe has at the same flow rate because the velocity in the 50mm pipe is reduced.


I would increase it to 50mm to reduce the velocity entering the tank. It will also allow you to harvest a bit more water during high intensity short duration rain events.