Rain water harvesting system

Hi all,

Just want to run my ideas about our rain water harvesting system past some experts here (SaveH2O et al) to reassure myself that it is an effective system before asking the plumber to execute the plan. Also to seek specific answer to some questions.

So, we're building in SE QLD. We've got a bit of a complex roof with top, upper and lower roofs (as you can see below).



We've got a rough total of 325m2 catchment area and about 110m of gutter length. I've tried to indicate positions of downpipes above with green marking.

Using BOM Design Rainfall Data System (2016) ARI 20 of 23.1mm and this online calculator (https://www.roof-gutter-design.com.au/Downp/applet.php), in conjunction with our drafter's drainage plan, I've figured out that my planned (14 + 2) 100mm DWV downpipes do exceed the minimum required to meet code.https://www.roof-gutter-design.com.au/Downp/applet.php

First of all, harvested water will be used for lawns/garden beds, topping up pool, as well as supplying toilet cisterns, bidet seats and for the washing machine.

Planning to run a 2 tank system, with a larger 10KL settling tank, decanting into a 5KL "clean" tank that'll be backed up by town water.



The pump drawing from the 5KL "clean" tank will be assisted by a ~ 100L pressure tank to reduce the start-stop cycles.

Question 1. Are leaf eaters mandatory for every downpipe? We're fortunate / unfortunate in not having any tall trees around us, so there will be minimal debris landing on the metal roof sheets...

Question 2. If we really do need leaf eaters, I do like the functionality of SupaDiverta, but not the bulk or aesthetics of it... Are there other products in the market that's less visually obstructing.

Question 3. Are there any potential issues with a hybrid dry (for lower roof on top of garage) and wet (top and upper roofs) system?







Question 4. If a part of the lower roof (above garage) is connected to the wet system (draining all the upper roofs), would there be any chance (in a severe downpour) that charged downpipes from the upper roof could generate enough pressure to reflux water onto the lower roof?

Question 5. Is it bad practise to discharge some water from the upper roof directly to the lower roof, even if the downpipe handling the lower roof can cope with the additional water?

I haven't had the chance to fully digest SaveH2O's first flush system. Also going to look at the TankVac overflow system.

Lastly, is a ball valve type mechanism the simplest way to ensure automatic top-up of "clean" tank with town water when it runs dry?

Appreciate anyone's thought about my plan.

Kevin

More pics

Hi Kevin,

I won't be able to answer this for a few days due to medical reasons later this afternoon. I also just noticed another thread awaiting an overdue reply I need to do. Should hopefully be able to do both on Saturday.

How many DPs do you plan to harvest?

Which is an average rain intensity of 4.62 mm/min over a 5 minute duration which is used to qualify for your area's 1:20 year storm event on which eaves gutter and downpipe compliance is based. Just be aware that despite the high intensity, it is still only the minimum qualifying intensity to be classified as a 1:20 year storm event. During a 1:20, you might be 1/4 way up the scale or just under 1:50 qualification yet still be in a 1:20. Never design for the minimum.


You need to check the regulations for bidet seats. As far as I know, only mains water is permitted.

Always good to see best practice used and a decant system is very effective.

I suggest also having a floating intake filter hose connected to the balance line valve inside the settling tank, this is done when fitting the valve. An irrigation shop will usually make one for you or at least supply the fittings.

We will have our own version out next year and it is planned to have 200 micron filtration plus some other worthy points of difference to other commercial products.

Good idea.

You usually have the tank's pressure set at 2 psi under the pump's cut in setting.

The tank need to have its pressure checked at least annually, the system and tank need to be drained to do this.It is wise to have a ball valve fitted upstream of the pressure tank to make this easier.

Not under the regulations but in northern areas, Health Dept and council mandates for leaf diverters to be fitted to downpipes supplying a wet (charged) system are invariably in force. The prime focus is to stop mosquitoes breeding in the standing water.

My own opinion is that leaf diverters should be fitted to all downpipe connecting to a wet system, no matter where you live.

The Supadiverta is Worlds best, it was engineered, not designed. It has an optional 100mm first flush plus ongoing sediment extraction during the entire rain event, can substitute as the tank's visually obstructing overflow pipe, eliminate the ugly vertical riser, increase the tank's storage capacity, oxygenate the lower stratified water layers which also decreases the stored rainwater's natural acidicy and prioritises outflow to different areas and tanks.The carrier pipes can also be plumbed along their length to supply hoses when required rather than gravity feeding from a remote tank or connecting to a pump.

Some buyers have a flashing made by a roll former to cover the vertical drops. These are mostly Colorbond but some plain flashings are rendered.

25mm pipes look more purposeful than the 20mm ones.

BELOW: A vertical riser, first flush and overflow pipe plus a sump between the DP and the riser on a standard system.

Also note the copper pipes, a no no to use with acidic rainwater!

Another big no no is having the vertical riser discharging water near the submersible pump as also shown.

Also note the overflow pipe has minimal mitigation and the tiny but ineffective first flush that will only fill with the settled water in the riser when it rains. Absolutely worthless! Unfortunately, the installation bad practices shown are typical.

The only leaf diverter I recommend is the steep sloped ICON Leaf and Debris Controller but I will possibly/probably finally release my own leaf diverter late next year. It has been a long term project that stalled late 2015 due to being unable to plastic injection mold the filter screen but advances in 3D Printing and materials may soon make commercialisation possible.

It will have 3 stage filtration with water flowing evenly down the entire surface area of a highly efficient small steep sloped 500 or 600 micron filter.

No gentle sloping mesh or screen cavities on ours!



No but water should not fall near the valve that supplies water to the pump. Fortunately, you will have a settling system.

The inflow capacity must not exceed the tank's overflow capacity.

You will only need an overflow pipe on the settling tank.


That depends on the hydraulics. If the system is correctly sized, that won't happen plus leaf diverters also serve as air gaps.

Roof drainage calculations factor several things including wind driven rain on abutting walls and additional water from a higher roof area draining to a lower roof. Compliance however does not guarantee good design and one of the worst yet compliant common designs has a concentrated flow of water discharging from an upper roof (see upper left in photo) to one end of a lower long gutter where there is no downpipe because aesthetics determined that the doiwnpipe should be around the left corner at the other end of the gutter. Unsurprisingly, this often results in the gutter overflowing.


For what reason?

Like the APEX Rain Aid? Yes, simple and cheap. The pump is always operating but the pressure tank will more than offset that.

Hi SaveH2O,

Bit of an update! What I thought were 2x slimline tanks are actually individual 2.5kL round tanks by however many I want to string together! So we’ve decided on 8 x 2.5kL, arranged differently around the garage (5x on west, 3x on south).

And herein are some questions I have with the new setup.

As these are individual pods, each acting as settling tanks, would it make sense to have in-flow from each end of the separate banks, with the outflow to pump from one of the more central tanks (as indicated).

Also, plumber indicating that he thinks the DIY sediment trap is too complex and not necessary... He said council regulation is for a knife gate valve on the storm water run-off. Having it closed most of the time, and when it pours or when we need the charged system flushed, open it up, and that'll suffice in getting rid of all the gunk. Somehow, it also makes some sense to me, particularly with our clean catchment (no large trees nearby), multiple settling tanks present, by the time water makes it to the central tank, it'll be pretty clean!

What size connection would you recommend between the tanks? 50mm?

Would it help if the balance valves between the tanks reduce in height from the outer most tanks to the inner most?

Would a 100mm horizontal DWV pipe be sufficient to carry water from 6x 100mm downpipes to the collecting tanks? Seems like the plumber is thinking that'll be sufficient... Or should I ask for 150mm DWV pipe?

Sorry for the delay, I am working long hours 7 days and cannot catch up with the back log but I finished a big project on Thursday which is good. Two previous posting attempts unfortunately failed, one was when I pressed submit only to find that I had been logged out of the forum for some reason and another time when I fell asleep reading through the earlier posts and woke up at 3:25 am. That's life!

EDIT: Well, it logged me out again but this time I kept a copy!

Your posts have highlighted the deficiencies of standard rainwater harvesting systems and so I will go over issues that you need to realise and factor.

You are in a high intensity rain area and you are harvesting several downpipes to each bank of 2.5K tanks.

If you divert water to just one tank on each bank, you will need just the one overflow pipe on that tank but unless that tank is raised, the water in the other tanks will settle to the level of the primary tank's water level at the overflow outlet's invert.

You need to calculate the overflow pipe sizes to discharge the design rainfall inflow. I don't know the tank's design but as an example, if you have a 100mm passage through the overflow outlet and let's say there is 125 mm of water above the pipe's invert, the flow will only be 5.72 lps which is a tad more than 340 lpm but that is through an unmeshed outlet. You can however have an unmeshed outlet by fitting an air gap to the vertical overflow pipe, something that is usually mandatory for QLD anyway.

https://rainharvesting.com.au/products/ ... ap-family/

You can boost a tank's overflow discharge rate by fitting an outlet fitting lower down the wall but fitting a upturned (vertical) elbow inside the tank instead of having a less efficient horizontal outlet. The elbow's crest would be at the same height as a horizontal outlet's invert and so you will have the better efficiency that comes with a vertical pipe while retaining the same storage capacity. A 100mm vertical reservoir wall with 125mm of water above the inlet will discharge at 7.38 lps or 443 lpm.

https://www.bunnings.com.au/rain-harves ... lsrc=aw.ds

With water flowing in so fast during a high intensity rain event, the balance pipes also become an issue when the primary 2.5K tank will fill within minutes plus turbulence will negate any perceived benefit of the settling system. Settling systems work best when the primary tank is a large tank. I would probably have a 40mm manifold balance system with ball valves on the assumption that any heavy rain would be of a reasonably long duration. It is also best to use UV stabilised flexible hose rather than a hard couplings plus also use poly nut and tails on the ball valves. You will also need to use poly nipples to connect the nut and tails to the ball valves.

It is in breach of regulations to harvest stormwater.

Roof drainage regulations end at the downpipe and stormwater drainage starts at the tank's overflow outlet. The pipes between the downpipe and the tank are not covered by either regulation but builders and plumbers (and councils) often wrongly quote stormwater regulations when referring to the rainwater diversion pipe. Sub surface stormwater pipe regulations for example use 1:100 ARI figures plus stormwater pipes include surface drains and silt pits!

One of the BIG problems with this misunderstanding is when plumbers use large pipes all the way from the head of the wet system to the tank. In your case, the plumber may intend using 125mm or even 150mm DWV pipe that has an inside diameter (ID) of 151.6 mm which is a volume of 18.16 litres per metre. Whereas stormwater pipes have to be laid with a slope, pipes diverting rainwater to a tank don't.

Flooded pipes flow differently to stormwater pipes laid with a slope because whereas non turbulent flooded pipes flow in boundary layers (or streamlines) and flow fastest through the core with the water on the boundary layers (walls) stationary, stormwater pipes flow as a channel flow along a curved bottom which achieves the recognised required minimum flushing velocity of 0.7 metres per second with small flows.

What the above means is that wet systems designed to stormwater regulations have very slow velocity at the head of the system, allowing accumulated decaying detritus to accumulate. As an example, a 150mm DWV pipe with a flow rate of just 0.5 metres per second = a flow rate of 545 lpm. You would never see this flow rate at the head of the system plus a velocity 0.5 mps is an inadequate flushing velocity anyway. Of interest, the commonly used 100mm DWV pipe has an ID of 104mm and a volume of 8.5 litres per metre. A velocity of 0.5 metres per second = a flow rate of 255 litres per minute.Properly sizing wet system pipes is vital best practice.

Sludge comprises of a lot of bacterial die off, the same as human and other animals poo. It is the build up of sludge at the head of wet systems that make wet systems retain poor quality water.

If you use leaf diverters, you can use smaller pipe at the head which will ensure movement of detritus and better quality water.

Another problem with standard wet systems is that they effectively destroy the stormwater system. These are all factors that you need to consider along with the need for adequate overflow from the two primary collection tanks.

Using leaf diverters also allows you to use a low restriction inlet because the water has already passed through mosquito proof mesh. Connecting let's say a 40mm flexible hose between a tee via an invert taper to the 40mm manifold will allow you to supplement the inflow as well as reduce the water levels retained in the vertical risers and the dowpipes to the same height as the water levels in the tanks.

50mm is pricey but best. I would divert a hose off the riser to connect further down a 40mm manifold as the higher pressure than the primary tank can deliver will start prefilling the other tanks. Perhaps leave the end (pump) supply tank closed. and fit a floating intake filter to the prior tank. Out filter will be released later this year, it will most probably have 200 micron filtration plus be much better and cheaper than others currently sold. The filter itself will be able to be retro fitted, you can have an irrigation store make one without the usual stainless steel filter cage. It won't cost much. and you can just clip a piece of panty hose or similat over the end of the hose in the interim. Two parts on ours have to be 3D Printed and I haven't had time to set up a 3D Printing farm yet. It will also be released in line with a new website and it has been hard to find the time to work through that as well.

I would draw from the end tank.

Have all a minimum 120mm above the bottom of the tank. Tank suppliers measure from the middle of the hole.

You need to calculate the total roof area but remember that your 1:20 ARI is the minimum qualifying figure. Regardless, leaf diverters will prevent water backing up in the gutters.

100mm DWV pipe flows at 510 lpm with a velocity of 1 metre per second. You need to do your calculations. Also remember that standard wet systems discharge a solid mass of water into the tank from above the tank...it isn't gentle! Even with our Supadiverta system that diverts to a low restriction inlet valve which de-energises the inflow quite quickly with the low density water immediately rising through the higher density water, I design the inflow not to exceed 1 metre per second but water from a vertical riser has much greater impact. I would not push water with a velocity exceeding 1 metre per second out of a vertical riser.

Hi SaveH20,

Once again, your detailed reply has given me a tonne of information to digest.

So, what I take away is that most plumbers would just bury the same sized DWV pipe from the head of the wet system to the tank, resulting in insufficient flushing velocity close to the head… I wasn’t present to see if that’s what my plumber did, but I suspect as that’s the easiest option, that’s most likely what he did…

Secondly, for the overflow, either the first tank needs to be raised to take into account the invert of a horizontal overflow pipe, or we fit a vertical flanged overflow outlet.

Thirdly, the hose from the bottom of the riser that normally goes into the low restriction inlet, I take that into a 40mm manifold balance system feeding water into all but the draw tank. Are there ready made manifold balance system with ball valves that you can suggest?

Lastly, without your DIY sediment trap, are there anything I can ask the plumber to do now to get rid of sludge that will inevitably collect as there won’t be adequate flush velocity in those pipes? Or would I just wait for a downpour and open the knife gate valve to flush the pipes?

PS. Plumber really against idea of pressure tank… He said it hides leaks, and requires regular inspections / servicing

Plumbers are not trained in rainwater harvesting.

I always try to explain the 'science' and quote the regulations or lack of but educating individual plumbers and builders is difficult when so many are set in their ways and won't admit ignorance. It is easy to find examples of the most basic mistakes on plumber's website galleries who for sometimes decades have claimed to be rainwater harvesting experts yet habitually install woefully sub standard and unnecessarily expensive systems.

When plumbers plumb a rainwater harvesting wet system, they effectively remove the stormwater system in that area!

Plumbers plumb and size wet system pipes as they would a stormwater system but wet system rainwater pipes between the downpipe and a water tank are not mentioned in the NCC Part 2 (BCA), the NCC Part 3 (PCA), AS/NZS 3500.3 and AS/NZS 3500.1. They are private pipes on private property but few industry 'professionals' realise this. If nothing else, plumbing large flooded pipes that do not flush and promote stagnation also fails the NCC Part 3 Performance Requirements that state:

“Performance Requirements
BP6.1 Stored rainwater
(1)A rainwater harvesting system must be designed, constructed and installed in such a manner as to reduce the likelihood of stored rainwater becoming contaminated or otherwise posing a hazard to public health.
BP6.2 Rainwater harvesting system installation
(1)A rainwater harvesting system must be designed, constructed and installed in such a manner as to—
(a)avoid the likelihood of contamination of water within the rainwater harvesting system, the water service, or the Network Utility Operator’s drinking water supply (if connected);

Standard wet system installations are recognised hazards and without doubt, the plumber would have laid the same size subsurface pipes the entire length.

A vertical flanged elbow overflow should not be fitted to the same height hole as a horizontal outlet because the weir's crest (the top of the vertical section) would be about 120mm above the height of the outlet hole's invert. The higher the water is above the 'weir', the more flow capacity you have but fitting a vertical flanged elbow raises the weir height which isn't good unless you have a tank with a domed roof and a high meshed (basket) inlet that still provides a reasonable height of water above the 'weir' before the tank overtops. Are you able to post a photo of the actual tank design that shows the overflow location and top meshed inlet's position?

Your primary fill tank's correctly designed overflow capacity is vital to prevent overtopping. If you work out your inflow rate to each bank plus a safety margin during a 1:20 ARI, I will be able to tell you the size overflow you require and the flow rates with different heights above a vertical elbow's crest. Getting the overflow right is critical for your system but I need to know the tank's overflow position and the roof design.

The two primary fill tanks would only need raising 100mm or so. The other tanks water levels will settle at either the level of a horizontal invert or a vertical elbow's crest but the other tank's levels will need mitigation above this level to match the fill tank's extra height of water above the invert or crest during heavy rain. Obviously there would need to be a different calculation made for a tank that has a domed roof and a high meshed basket intake than would be for a tank with a flat roof.

I made a mistake with that recommendation. Our systems don't require overflow pipes whereas your system does and I was thinking about what we would normally do. You can however fit an inline valve to manually open or close the low restriction hose when needed, I have this on one of my 4 tanks when I want to divert water from other pipes supplying higher tanks but I only do it during light rain when needed whereas you would benefit most during heavy rain because of the massive amounts of water flowing into the two fill tanks. If it was permanently open, the additional tanks would be prime to overtopping because the vertical riser always has more head than the two primary fill tanks will ever have.

A secondary advantage of diverting some flow to the manifold is to lower the post rain water levels in the vertical risers and the downpipes to the same level as the water in the tanks.

You need to make the manifold balance system yourself. An advantage is that apart from the end tanks, each tank only needs one inlet/outlet valve which a tee would fit to. Sizing would come back to how quickly the tanks would fill and cost, for example, would you want to have ball valves at each inlet valve. The manifold's main line would however usually be larger than the branch line and the ball valve and inlet fitted to each additional tank because they are balanced multiples.

If he has installed it as per stormwater regs, the pipe will have a slope and a sliding gate valve will be reasonably effective. The sediment trap wastes a lot less water but you will have huge excess to your storage capacity and so waste is not a consideration but because the plumber would have no doubt have installed large pipes, a properly set up flush outlet would now be the better option. Most people on level blocks don't have this option and wet systems are 'drained' via uncapping an inspection outlet fitted to the vertical riser. This is messy plus the subsurface pipe ramains full of water anyway.

Complaints about pressure tanks usually relate to the bladder or diaphragm failing but this is because people often use cheaper tanks with cheaper industrial rubber bladders or diaphragms. Rainwater lacks minerals and will draw elastomers from the rubber, tainting the water as well as making the rubber brittle. Rainwater should only be used with tanks that have a butyl bladder or diaphragm.

The pressure is recommended to be checked every six months but once a year is usually ok. To check the pressure, the system must be drained, don't make the common mistake of checking the pressure when the system is pressurised. It is easy to install a ball valve to the pipe to drain the system. The pump's cut in pressure must also be 2 psi above the tank's pressure so that the tank still has water in it when the pump kicks in. The pump's cut in setting must be fit for purpose when retro fitting a pressure tank.

The tank will have a schrader valve at the top and you can fit a small pressure gauge to it in any case. If there is a leak in the system, the pump will occasionally start to re-pressurise, that is not hiding any leak that might happen! Most often the leak will be a toilet cistern valve set too high at the air gap.

I sell pressure tanks including 60L and 80 L Pressure Wave but I also have 165 L American ones. What are you paying for the 100 L one? The 165 L ones have a 1.25" NPT thread but i have 1.25" x 32mm BSP brass adaptors. You would use an additional 32mm x 25mm poly nipple if you were using a 25mm hose to supply the pump.

Re 25mm hose, not sure if I have already posted this but be aware that the commonly used 25mm Blue Stripe poly hose has an internal diameter of 21mm.

Further update.

Absolutely disappointed at my plumber!!!

I sent a lengthy email to the boss detailing what I wanted done for the rainwater harvesting system with diagrams, explanations, and they just did what they’ve always done and not what I wanted.

So, 8 tanks all level, connected in series, 3 overflow pipes (not vertical flanged), 5 inlet sites (3 wet, 2 dry), no low restriction inlets, no sediment traps, pump without pressure tank (with 90 degree elbow 10cm from the inlet!). When confronted, just said he’s got the experience and knows what works and what doesn’t. And when I questioned him about detrimental effect of having an elbow so close to the pump inlet, said he’s never heard of it!

Is there anything I can do about my situation?!

The best thing is to fit a good floating filter in the tank that supplies the pump. These are also called floating suction filters, floating intake filters and a few other things. I will be releasing one soon and will most probably refer to it as a Water Tank Floating Filter because I believe it is a more readily understood term and better than the Fina Filta Floata TradeMark I was toying with lol.

A floating filter is a hose that is connected to a buoy at one end and a low drain valve at the other end. There is a 'filter' fitted to the end of the hose at the buoy end and this is 200-300mm below the water surface where the best quality water is. The tank outlet delivers water via the usual hose to the pump.

There are quite a few sold now but they are pricey and most also have faults.

1. Water passes through mosquito proof 955 micron mesh when entering the tank but many floating filters sold have an expensive 1,200 micron stainless steel mesh filter which renders them useless and if you do rub it to clean it, a lot of muck simply falls into the filter.

2. Many of the filters will settle on the sediment layer when the water level gets low because they are not fitted with a support disc that keeps the 'filter' raised.

Mine won't have these faults but it will still be cheaper plus I am looking at the choice of 200 or 400 micron filtration.

To fit one, you need to empty the tank and have a hole drilled that is then fitted with an outlet valve with the floating filter already fitted to it. Once there is water in the tank, you just make sure that the hose is flooded before switching on the power to the pump. There are instruction videos on You Tube.

Re your installation, having the elbow 10cm (100mm) from the pump's suction port isn't too bad but it depends on the hose's internal diameter and the velocity through the elbow of course. If the pump only supplies cisterns, no problem because cisterns only fill at 6 lpm. A lot of "know everything" plumbers fit the elbow directly on the pump's suction port!

Does the plumber have a website complete with a gallery of his 'workmanship'? I would love to have a look.

Also read the post linked below re 10 endemic mistakes that plumbers make just with a water pumps! BTW, there are more than 10 but 10 is a nice number.

viewtopic.php?f=35&t=103597&p=1897978&hilit=blue+stripe#p1897978

Next links are to forum members long term experience with sediment traps. Super simple and super effective.

https://forum.homeone.com.au/viewtopic.php?p=1551215#p1551215

https://forum.homeone.com.au/viewtopic.php?p=1146540#p1146540

A wet system does not flush, it drains. Once the hydraulic head in the downpipes has drained, there is no flushing velocity and wet system pipes are usually lengthy.

The next thread's OP made his own floating filter. Worth a read and there are photos. It is a copybook system.

viewtopic.php?f=35&t=97686