Water tank and pump configuration

Good morning all.

Long time reader first time poster.

I am after some advice on configuring water tanks for a build in victoria. We have a half acre building envelope that slopes down left to right.

I am going to have a large shed. 190m2 with a large 90k water tank in front of it. This will be situated on the higher ground. About 7 or 8m away will be the house which will be 130m2. This will be downhill from the larger tank so i was going to have 1 or 2 smaller tanks (2k tanks) situated next to the house.

My first unknown is is it better to have the smaller tanks on the lowest section of the house so all home downpipes can flow into the tank. 1 or 2 pipes on the other side of the house will have to go around the house.

Now with transferring water is it best to have a transfer pump operated by floats at the smaller tanks transferring to the bigger tank. Or is it better to have a solonoid valve gravity feeding water from the 90k tank to the smaller tanks.

Which ever way i go i will have a variable speed pump distributing the water into the house.

Any tips greatly appreciated.
Cheers

Will you also be on mains water? I am assuming not.

I am also assuming 3 or (possibly) 4 downpipes at the house.

No mains water just tank water.

Yes 3 downpipes total. 1 on either side of the house (2 total) with a butterfly roof and box gutter down the middle. Then 1 downpipe on an alfresco roof.

Would you consider having one of the two tanks at the house larger than 2,000L?

I don't know your average annual rainfall but your catchment area totals 320 sq m. This will give you a yield in Victoria of about 85%. For every 100mm of rainfall, you would collect approximately 320 (sq m) x 100 (mm) x 0.85 (yield) = 27,200 litres or about 74.5 litres per day.

For rainwater harvesting best practice, I would not pump water to the 90k tank and I would use one of the two planned 2,000 L tanks as a second settling tank that captured most of the water from the house. Let's make number 1 the 90k tank, number 2 the settling tank and number 3 the tank that supplies the pump.

I am assuming that tanks 2 & 3 are on bases that are the same height.

I would also use leaf diverters to prevent solid bird droppings and other muck washing into the tanks. The only leaf diverter that I recommend is the ICON Leaf and Debris Controller, it is $38 at my local Big Green Shed. Beware of other leaf diverters that do not fully drain or shed leaves which causes splash and yield loss.

TANK 1
This would obviously be supplied by a dry pipe infeed but do not have the top meshed inlet above the outlet that supplies water to the bottom 2,000 L tank. This may sound obvious but I see this mistake all the time.

If you intend fitting an overflow pipe to this tank, then also have the top meshed inlet fitted within arms reach of the overflow outlet so that you can access the mesh for cleaning.

You only need a small pipe connected between the larger tank and the bottom settling tank. This will retain less water and turn the water over faster plus the faster flow will purge the pipe of any possible (but not probable) debris. To draw the best quality water, the outlet valve should be about 300mm above the bottom of the tank.

You would also most probably want a larger outlet valve fitted close to the bottom of the tank for other purposes. Are you in a bush fire zone?

Rainwater is naturally acid. To raise pH, you can put a heap of limestone chips in a nylon bag and lower it to the bottom of the tank. Just tether a buoy to a line for access if ever required.

Also cut out an oversized piece of shadecloth and place it over the tank's top meshed inlet to make cleaning the mesh easier and to also restrict sunlight ingress.

TANK 2 SETTLING TANK
This would collect from two downpipes and I assume that the box gutter will harvest a larger roof area that either of the other two downpipes. Yes/No? If Yes, it would supply the settling tank.

The purpose of a settling tank is to supply the tank supplying the pump with good quality decanted water.

I would have a valve fitted 200 mm above the bottom of the tank which would cut in at 450mm and fill the tank to about 500mm. This valve would receive water from the 90k tank.

An outlet valve would also be fitted about 200 mm above the bottom of the tank and this would supply tank 3.

Because this tank would receive water from 2 downpipes, it must have enough mitigation to store water from a reasonable amount of rainfall. If the tank was 2 m tall, its mitigation would be approximately 1,500 L.

TANK 3
The inlet valve from the settling tank would be about 200 mm high, the cut in would be 400mm and the cut out would be about 450mm.

This tank would be supplied by one downpipe and the valve's top up levels would ensure that minimal water from the settling tank entered when it was raining.

The 400mm cut in also ensures that the pump would not be drawing a free surface vortex.

A variable speed pump is ideal for off the grid use and well worth the additional cost. Highly recommended.

I haven't mentioned first flush diverters. If you choose to have these, just be aware that having one with a dripper will result in a lot of yield loss, you need to have one that is manually drained which also enables you to use the captured water.

I hope that this helps.

Thank you for the reply. Greatly appreciated.

Yes we can have greater then 2000L tanks at the house. Probably up around 5k will be fine too.

"This would obviously be supplied by a dry pipe infeed but do not have the top meshed inlet above the outlet that supplies water to the bottom 2,000 L tank. This may sound obvious but I see this mistake all the time."

I am a little confused by this. Are you saying have the inlet from the downpipes to the large tank lower then the outlet??

Yes in bushfire zone. Will have cfa outlet on 1 or 2 of the tanks.

The Box gutter will collect roughly 90m2 of the 130m2 roof so yes tank two will catch most rain water from the house.

I am thinking that you are saying to have solenoid valves between tanks 1-2 (located closer to tank 2) and also another solonoid valve located in between tanks 2 and 3? Is this correct? Do you have recommendations for a solenoid valve and/or floats?

Thank you again for all your help.

The settling tank will need to be larger to accommodate the inflow, if not, you are restricted to either pumping to the 90k tank or else overflowing somewhere. Much easier to have a larger settling tank with good mitigation.



No. What I am saying is that if the tank's top meshed inlet (where the water falls in) is fitted above the bottom outlet valve that will supply water to the number 2 tank, the water falling in this area will stir up any sediment when the tank's water level is low. It is better to have water falling through a tank's top meshed inlet that is well away from that area.

Actually, the water level doesn't have to be all that low for it to cause sediment resuspension due to the generation of impacting toroidal vortices. I can post some information about this subject if you like, it is quite fascinating.

With regards to the outlet valve, a lot of tanks have the valve that supplies the pump fitted very low on a tank which then draws the worst quality water and any suspended sediment from the tank. It is a common yet obvious fault.






Topaz had a nice small valve that operated with low pressure, they might still make it.

There are different valves, the one fitted to tank 3 just needs to supply a water level that is no less than 200 mm above the valve that supplies the pump and the tank 2 settling tank level should be a bit higher than tank 3. I prefer a set cut in and cut out height because it gives a good continuous flow through the pipe but that may perhaps be a bit pedantic. The required mitigation capacity of tanks 2 & 3 will determine the cut out levels to a large degree.

EDIT: Most solenoids need a minimum 20 kPa pressure to operate but maybe there are some new ones that don't. I think that a manual valve is the way to go but you need one that operates on very low pressure. The critical one is tank 3.

Ok, so things have changed a little since back then. I have attached some pictures of plans to hopefully make it a bit clearer.

I am trying to work out how to get the two rear downpipes to drain water into the two 25k tanks at the front of the shed. Here is the information

- Grantville Vic ARI is 115mm/hr
- Roof catchment area 180m2 so 90m2 on the shed rear.
- 2 x 90mm downpipes in corners of shed rear
- 1 x 100mm DWV pipe carrying water underground, sloped 1:100.
- Shed gutter height 3600mm
- Water tank height 3070mm
- FFD and leaf eater's will be fitted.

Obviously with the leaf eaters i am not leaving much head pressure to push the water through. I am wondering if the head pressure will be ok or if there is another solution. I might be able to change water tanks to the squat tanks which would give me an extra 470mm but not sure the tank company will be overly impressed.

This is a very common problem and the reason why a lot of people don't fit leaf diverters to the top of wet system downpipes. If at all possible, they should be fitted to prevent mosquitoes and other pests accessing the standing water.

Your wet (charged) downpipe diversion will discharge into the tank's top meshed inlet but I don't know the inlet's height. Is it at the very top of the tank?

What type of base will the tanks have and will this add to the tank's height?

The head is calculated from the top of the wet system's vertical riser above the tank's top meshed inlet to the overflow point on the downpipe. If you allow for 50mm above the inlet's rim, you will have an additional 150mm head loss during a major storm event. Many persons (plumbers included) measure from the inlet to the gutter's sole which is wrong.

The photo below shows a neatly installed vertical riser but note the closeness of the100mm pipe to the meshed inlet's rim. Before securing the riser, you need to make sure that the cover can be removed if ever needed. This installation had just enough room to do this.

If we take the height of the vertical riser as 3.2 m and the height of the Leaf Eater's overflow level as 3.4 m, then you will only have 200mm head. The height of the vertical riser depends on the tank's top meshed inlet's height and any height impact that the tank's base will have but we will use a 200mm head as our example here.

The wet system will have friction losses from the pipe plus friction losses from fittings (tees and elbows) expressed as equivalent lengths of pipe. The pipe friction loss as an equivalent length of pipe from the nearest charge point will be (as a guesstimate) about 45 m.

I will use a worse case scenario of 200mm head for this example and 45 m of friction loss.

The Hazen-Williams is a good calculator to use for this situation.

http://www.calctool.org/CALC/eng/civil/hazen-williams_g

The 100mm SN4 DWV pipe's internal diameter is 104mm. We need to change cm to mm.

The roughness coefficient has to be changed from 140 to 150.

The discharge rate has to be changed to litres per minute.

As per the screen shot below, I have also entered a 0.2 m head.


As you can see, the flow rate is about 350 l/m which coincidentally matches your minimum 1:20 ARI roof capture from all 4 downpipes but I have assumed that the other two downpipes will be a dry system which drain separately.

For added interest, I have also pasted the flow rate through a 90mm stormwater pipe plus additional information.

213 l/m.

The 100mm DWV pipe has about 46% more volume than a 90mm pvc stormwater pipe.

If you double a pipe's internal diameter, you increase the volume x4 but if the same head is used, you increase the flow rate by about x6. In other words, for every 1% increase in volume, the flow rate increases about 1.5%.

On another note, to double the flow rate, you need x4 the head which is why low head pressures are still quite efficient.

If our 100mm pipe's example had a 0.3 m head, the flow rate would increase to about 435 l/m. See below.

A tank's head however can be supplemented by plumbing a Low Restriction Inlet off the wet system PLUS there are additional benefits by doing this even when a tank has an adequate head. This improvement to a standard wet system came about through the research, development and success of our 3 in 1 Supadiverta rainwater harvesting system.

A low restriction inlet is a valve fitted a minimum 100 mm above the bottom of a tank and connected to by a flexible hose that diverts water from a junction fitted to the wet system. The tank's inlet valve is typically 40mm or 50mm but you will have 65mm fire fighting valves fitted to your tanks anyway. If you don't use a fire fighting fitting, a 40mm valve would provide plenty of flow.

The wet system's vertical riser will always operate with the same limited head pressure dictated by the riser's height above the tank whereas a low restriction inlet will operate with a variable head due to the changing height of the water inside the tank. The low restriction inlet will always operates with more head pressure than the vertical riser.

The weight of the water in the tank DOES NOT push against the water flowing into the tank...a common misconception! Water reacts to the pressure exerted by a column of water which is 9.82 kPa per metre.

An inverted taper is used to reduce the wet system's connecting junction to the required size. They are available in various size reductions.

OTHER BENEFITS

Oxygen rich water will flow into the tank's anaerobic zone, freshening the water.

Water won't drop from a height into the tank and cause sediment resuspension.

The water in the wet system won't be retained to the level at the top of the vertical riser after rain, it will only be level with the water in the tank. This exposes less water held in pvc pipes above ground to the elements.

Easy and not costly to do.

FOOTNOTE:
Provided you have enough head, you should look at the ICON Leaf and Debris Controller at Bunnings. It is about $38 and is the only one that I recommend from the current bunch of leaf diverters.

It has a straight , flat outer screen that isn't wire mesh. Debris adheres to the usual wire mesh used by most others because water cannot get under the debris to wash it off whereas the ICON diverter has a triangular ribbed surface running downwards at a steep angle and a large internal mosquito proof wire mesh that pulls out like a drawer for cleaning. The outer flat filter is also very easily removed for maintenance.

Just be aware that 'some' other leaf diverters have flat wire mesh in a recessed section at the bottom plus 'some' also don't fully drain.

The ICON unit is bigger which means a bit more head loss, just do the maths to judge whether suitable.

Great thank you for that SaveH20. Your a good man.

Exactly what i have been looking for and i will definetly be putting in the low point inlet also. Have also made some floating suction hoses DIY style as the price of commercial ones was rediculous for what you get.

I have purchased the Rain harvesting leaf diverters which were $38 from bunnings, they have the wire wesh then the inner mozzie proof mesh. I cannot find the icon leaf and debris controllers online anywhere. Do you have a link available?

Also i would like to put a low point bleed on the charged system but getting to the lowest point is quite difficult if i run 25m of stormwater at 1:100 that is 250mm depth difference from one end to the tank. Do you have any suggestions?

Cheers
Aaron

I agree. They use to cost about $250, a few places copy them now and prices have dropped but you still need to pay at least $170. When I get around to it, I intend making my own and sell them for a more realistic price.

Just make sure that the intake on yours is about 200mm under the surface for the best result.


Bunnings sell them for $38. They are a larger unit because the outer filter is straight. It is made by Icon Plastics at Hallam, Victoria.

The smaller stormwater pipe requires a minimum 1:100 slope because it must drain and also flush debris. While the pipe will be considered to be part of the stormwater system IF the overflow connects to the council stormwater system, it is still a wet (charged) system that will remain flooded between rain unless it is drained. Basically, you can have the low point at whichever end is most convenient for you.

The water in the wet system will also be much, much cleaner that what is retained in a normal wet system because of the leaf diverters, necessitating far fewer flushes. There are also options as to how you flush the pipe. You are not restricted to a large discharge to a small area.

Re your planned 90mm first flush diverters, the standard 90mm first flush diverters are not much cop for the following reasons.

1. 90mm stormwater pipe is the outside diameter, the inside diameter is 86.2mm which has a volume of 5.8 litres per metre. If you know your roof areas, you will see how little rain is actually collected as first flush.

2. 100mm DWV pipe has an internal diameter of 104mm which gives a volume of 8.5 litres per metre. This is 46% more.

3. First flush diverters usually have a hole in a washer that is called a dripper but many run as a constant fine but fast stream, wasting 4-6 litres per hour. For Victoria's rainfall pattern where most rain is drizzle or light interspersed showers over long periods, this can severely deplete yield. Melbourne averages 147 days of precipitation per year over many, many hours.

4. Cleaning usually requires the unscrewing of a bottom cap which can get very wet and messy.

You can convert a 90mm stormwater pipe to a 100mm DWV pipe by using a 100mm x 90mm pipe adaptor.
https://www.bunnings.com.au/holman-100m ... r_p4770444

Having a 100mm DWV pipe would allow you to use one of our bracketed 100mm support caps that drains through an outlet tube that you can fit a 19mm poly pipe to. This greatly reduces yield loss by eliminating the dripper plus the need for cleaning maintenance. It also allows you to use the flush on the garden. Note that this photo was taken immediately after fitting, the pipe isn't painted and the poly pipe isn't secured to the wall.

If you will have sufficient head, then this small improvement will reap significant long term benefits.

Yep have purchased some food grade suction hose, some floats, strainers and stainless steel wire. Reckon the cost for me to make two is less then $100.

This is the one i have bought, it looks very similar to the icon drawing on the icon catalogue website.

https://www.bunnings.com.au/rain-harves ... d_p4774053

Great i will use 100mm for the FFD abd grab some of those brackets from your wesite also.

Cheers
Aaron

They were about $240 when they first came out but a lot of places have copied them since but the cheapest is still about $240. When I get time, I'll make them myself and sell them for a more realistic price.

The problem with the one linked is that solid bird droppings fall through the course outer mesh and wash through the inner mosquito proof mesh.

The ICON one is below. It was designed in NZ and the original outer screen wasn't something that I would put my name on. The current outer screen is much better.

I have linked an eBay seller below who is charging more than double what the latest version can be bought for in Bunnings. Note the old honeycomb outer filter design!

https://www.ebay.com.au/i/252601999957?chn=ps

I can't find a photo of the latest screen, only the sketch below. I will take a photo of one tomorrow.

They are not available on the website because they are manufactured in a family die as two non matching caps and if I sell them, I am left with an unusable cap. Just contact me and I will send you some.

Also have you done a DIY on a tank Vac system, another rediculous price for some PVC pipe with holes in it?

The total cross sectional area of the holes (suction velocity) is vital to match the discharge flow rate plus you have to have a vacuum break at the top of the internal overflow pipe so that the tank doesn't syphon dry. I can make something that will purge the outside pipe to create the syphon easy enough.

I have no plans to DIY one though, my Supadiverta system eliminates the need for an overflow pipe and very little sediment builds up in the tank, what is there is like talcum powder, just the settled fine suspended particles that passed through.

I intend having the website show a simple plan for a similar floor vacuum that simply connects to a very low inlet that people can open once a year or so when the tank is full and rain is expected. It won't be an overflow, just a simple tank cleaning system.

It isn't worth my while selling it as a kit, just easier to show some diagrams.

Ok well that probably makes it a bit more difficult. There are cheaper options such as these, but these do not have a pipe accross the tank floor. It will only take it from one spot.

http://www.enter-shop.com.au/catalogue/c2/c13/p108

I have a very simple tank cleaner design that is like a vacuum head that you push slowly over the floor and it works well. In time I will have it on the website at a cost including postage that will be cheaper than someone buying the parts and then having to calculate suction angles and velocities.

You can fit a simple and inexpensive DIY sediment trap to a non turbulent section of 100mm DWV wet system pipe that will capture the bed load and discharge it manually through a reduced sized pipe. Bed load is settled suspended sediment and heavier debris that clumps in 'colonies' on the bottom of the pipe but when it travels and comes to the sediment trap, it simply falls down the 'hole'. The trap not only dramatically alters the amount of sediment that is common to rain water tanks, it also alters the type of sediment to something that resembles fine talcum powder.

We now use an invert taper and not a pipe reducer to downsize the pipe because the pipe reducer retains some sediment at the bottom below the outlet.

Reducing the pipe size increases the velocity, decreases the flush yield loss and allows the purchase of a smaller and cheaper valve. A 40mm DWV pipe holds roughly 1 1/4 litres per metre.

There is usually a low restriction inlet fitted and this is closed when the collected bedload is flushed.

A one year summary of a 4 tank system that used this sediment trap is linked below. See post 61. The happy home owner also made the above diagram! Thanks John.

viewtopic.php?p=1146540#p1146540

Here's how Ive done my rain water system.
Its similar in terms of have 2 tank sites and transfer between.
Im lucky not to have leaf problem.