Water tanks for the technically challenged

Since my last post on here quite a bit has happened. We complained to the Victorian Building Authority about the height of the pipes. I was expecting them to simply send a letter to the plumbers smacking them over the fingers but they actually contacted them and ordered them to rectify the work. I was pleasantly surprised but that didn't last long. The plumbers came and took a look and told me to raise the rainwater tank! They also took photos and argued to the VBA that we had changed the ground levels. Several months of arguing back and forth and I finally managed to supply the VBA with enough evidence to refute the plumbers. In the meantime we found more pipes at the wrong height as anyone who has read the Damp Proof Course thread would know.

Yesterday the plumbers came out to do some work. It had been agreed that the pipe on the NW corner of the house feeding the rainwater tank would be disconnected from the wet system and connected to the stormwater drainage. We were happy with this and here it is:





It was also agreed that the tank outlet pipe would no longer run around the back of the house but would go to the stormwater drain outside the garage.

What I didn't understand had been decided was that the charged system was going altogether. The argument was that we only need 50 square metres of roof draining to the tank but more importantly, we don't even need that, since the estate has recycled water. There are a few issues to argue about here but, at the end of the day, we were happy to see the charged system go because there is a much better alternative for us which we will implement later after we move the rainwater tank.

Here are some photos of the works for plumbing enthusiasts:

Downpipe outside garage now going to stormwater and vertical riser on drain which now looks like this:





New tank outlet pipe with inspection opening outside laundry door- the house is going to subside but at least the stormwater drainage is okay:









Vertical riser at tank gone:





They still buried the ball valve but I've uncovered it somewhat:





And they gave us a bonus drain for our hot water system which was draining into a piece of pipe stuck in the ground - or not draining actually; it had been full of water since it had been installed.

On our old house when we upgraded to solar hws, we got the storage tank placed outside, and the relief valve drain had to move, so they ran it to the end of the verandah, and put a short length of pipe underground so that we wouldn't get a wet patch. However this pipe only ran about 60cm in to dirt that was packed down.

The point I'm trying to make is that our one never filled up or really had any water left in it for very long at all. I'm guessing here, but perhaps your hws is set at too high a temperature, and therefore releasing more water than it should be. Perhaps even the ptr might not be 100% perfectly manufactured ?

Hi bpratt,

Our hot water system is gas only, no solar. It has a tempering valve on it and no water controllers so we can't vary the temperature at all. It does have quite a bit of acidic condensate because it is an enviro 26. It is also possible that, in the position it was placed in, it was getting filled with rainwater as well. I don't know if I have a photo of it full of water but it was brimfull.

This was taken before they did the work - you can see the bit of pipe in the background. It was full to the top of that with water. The plumbing inspector even remarked on it. There are no eaves over in that spot - I don't know if that is what made the difference.

The other possibility is that there is something wrong with the way this gas hot water system has been installed. It makes an audible noise inside the house whenever the hot water is turned on or off. You can hear it from one side of the house to the other. The builder, who recommended this unit, maintained that it was normal operating noise.

Hi Liliana,

They still covered the ball valve! Unfortunately, the regulations do not mandate against doing this. Some things just require common sense.

Looking at the photo, it looks like they have reinstalled the rainwater tank a non compliant distance from the windows but I am unable to find the regulation. I hope that someone else can provide this information.

The downpipe outlet above the tank's top meshed inlet also appears to be a 90 degree elbow. If it is, it could be too close to the mesh but this also isn't regulated. They should have used a 45 degree elbow if it is too close.

Your "bonus drain for our hot water system" appears to be uPVC pressure pipe.

AS/NZS 2032:2006 Installation of PVC pipe systems states that uPVC pressure pipes installed in direct sunlight must be painted with light coloured water-based paints or otherwise protected. Note that the pipe as used is not pressurised but uPVC pipe should still be protected from the elements regardless.

EDIT: Water tanks are defined as a structure – Class 10b under the BCA. Emailed and asked the VBA on Wednesday the question about how far a class 10 b structure must be away from a window. Still waiting.

EDIT 01/06/2014: Text tidy up.

Hi SaveH20,

And I was so happy! The plumbers can't do anything about where the rainwater tank is installed. It is like that on the plans and all the inspector can get them to do is to make the system compliant. He can't enforce anything in our contract either. So, even though we might have four downpipes going to the rainwater tank, as the latter is a contract issue and not a compliance issue, it has nothing to do with the VBA. He is bound to accept any solution that meets the regulations. We will move the rainwater tank because we need to organise the base. I did ring the council last year about the placement of the rainwater tank but they have no regulations governing distance from windows.

The ball valve - yes - but then I did hear the inspector having to explain to them that there has to be a 75mm separation between the top of the ORG and the ground and asking one of them if he really was a licensed plumber.

PVC pressure pipe?? That's interesting. All painting was supposed to be done by us so I can organise that. Thanks for the tip-off. But the pipe wouldn't get much sun. It is on the south side. Does it still need painting?

Hi Liliana,

That was quick.

I have seen a regulation re the minimum distance of a tank from a window but I have done a quick search and have been unable to find it. I have left a message with the VBA asking for clarification for both a fixed and an outward opening window.
EDIT: Never did find it.

uPVC pressure pipe only requires painting if it is in direct sunlight. It looks a lot better painted anyway.

Moving the tank when the time comes is no real problem.

How could the plumbers possibly justify the pipes being buried shallow by blaming it on the rainwater tank being buried?

Drainage plumbers should know about ground levels, ORG levels and maximum flow rates through pipes. It is the most basic of knowledge needed to do the job.

Here SaveH20,

Just for you:





My remaining concern (apart from the effect on the foundations of all the digging) is that some of the pipe seems to have been mainly covered with our crushed rock and not clay. But we can probably remedy this ourselves when we come to pave.

That's better.

The tank doesn't look so high either. Will post the advice from the VBA when i get it.

Hi SaveH20,

Just some clarification in relation to the pvc pressure pipe issue. This is a close-up photo of the pipe under the gas hot water heater.





It appears to be 100mm DWV pipe. So when you refer to it as "pressure" pipe, do you mean it can take a lot of pressure as opposed to being a gas pressure pipe or are you referring to the pipe attached to the hot water unit which is over the grate.

This is a close-up of the pipe outside the garage.

Hi Liliana,

I was referring to the smaller uPVC (pressure) pipe above the grate.

With pressurised pipe, it is obviously important to protect the pipe's structural integrity but protecting against UV degradation is also wise for uPVC downpipes even though they have UV stabiliser added during the manufacturing process.

Thanks for that. The pipe from the hot water system wasn't installed by the drainage plumbers; it was done by the other plumber after I informed the builder that we needed a condensate pipe on the hot water system. We'll make sure to paint it and all the other PVC pipes. It is on the to-do list which is still enormous.

Reviving this thread as we are now in a position to do something about sorting out our less than ideal rain water tank system. We are intending to move the 2500 litre poly tank to the easement for which we will have to get permission from City West Water. This will enable us to finish paving at the back of the house and will give us access to our windows and our weatherboards which need repainting. We are intending to replace the poly tank with a steel slimline tank so it can be positioned away from the house and near the fence. The slimline tank will then feed our poly tank on the easement. I have been informed by the Council that there are no regulations governing how close to the fence we can site our rainwater tank so that's a great help to us.

Our next problem is our pump which is fitted with a Vada rain2main automatic rainwater controller. The pump is situated right under our laundry window and at present the poly tank is about 1 metre away from the pump (1.2 metres if you take the outlet into consideration). We are now unsure just how far from the pump we can site the new tank without interfering with the suction. The instructions say the rainwater controller must have a minimum distance of 100mm of straight pipe at the mains water inlet but the pump instructions just say "find a location for your pump as close to your water source as possible". I've attached the technical data sheet for the Vada V80-H pump below:

Vada -v80-H

Just wondering if there is any rule of thumb for how far from the pump we can site this rainwater tank?

Interesting that they state this only for the controller's mains water inlet and not for the pump, not that I could see anyway.

One of the numerous mistakes that plumbers make is when they fit a 90 degree elbow directly to the pump's suction side when a straight length of suction pipe that respects 8 internal diameters (ID) should be used. Not all manufacturers include this in their fitting instructions and some only state 5 IDs but even when they do, plumbers will still use the 90 degree elbow.


Good question as it brings up an important matter.

Firstly, you have a good but unnecessarily powerful pump for use with low flow short duration end fixtures.

A jet pump sacrifices some pumping efficiency to boost performance on the suction side and are best for longer pipe runs but your pump is not a jet pump. This is not a real problem.

IMPORTANT BUT COMMONLY NEGLECTED:

Most pumps use Blue Stripe poly pipe which is nominally measured as an outside diameter. This means that the commonly used SDR 13.6 (aka PN 12.5) 25mm Blue Stripe poly has an ID of 21mm. This might not seem much but a 25mm ID pipe has 43% more volume than a 21mm ID pipe. This is substantial.

Most pump manufacturers state that the pipe's used must have an ID that is equal to or greater than the size of the pump's inlet and outlet. Your pump has a 1" female inlet and outlet.

Copied off the VADA pump link you posted:

4. Suction
This is the most important part of the installation as errors will cause significant problems for the system in performance and longevity.
A gate valve must be installed at the water source outlet. To maintain optimum performance from your pump, the suction pipe should be:
• Kept to the shortest length practical.
• Re-enforced crush resistant (non-collapsible) hose or pipe.
• All fittings should be air tight.
• Pipes should be equal to or larger than the diameter of the suction/inlet port.

The 32mm Blue Stripe poly has an ID of 27mm, a volumetric increase of 65% over the 21mm ID. For every 1% volumetric increase, the flow rate, unless restricted, will increase by nearly 1.5% at low to medium velocities due to less friction loss. This means that the 32mm pipe will have a realistic flow advantage of nearly double that of the commonly used 25mm SDR 13.6 Blue Stripe poly.

My suggestion is to upsize to 32mm Blue Stripe which should have already been fitted anyway.

I hope that this helps.

Wow - that is an incredibly detailed analysis of our pump setup. Thanks for taking the time to do that. So if we upgrade to the 32 mm blue stripe pipe do you have any idea of the maximum distance we could site the new rainwater tank?

Suction depends on the demand and your end fixtures have a demand of about 6 lpm. Friction loss at low velicity is minor.

I have posted a chart below that shows friction loss per metre through common low density garden irrigation (black) poly pipe which has an ID very close to its nominal size. You will see that there will be no drama having a long run to low fill demand end fixtures.

So if I understand that table correctly our pressure loss with the 32mm pipe is going to be less than 0.02 kPa/m. That's very good news.

32mm Blue Stripe has an ID of 27mm but the chart gives a good indication of the lesser friction losses with larger pipes. The chart shows common garden irrigation pipe, not Blue Stripe.

Do you remember the issue you had with the low flow out of the garden hose yet there was good pressure at the tap? It was all about friction losses through the 12mm hose.

I am trying to finalise the details of our new rainwater harvesting system before we start landscaping. We intend to use three Supadivertas (see https://www.supadiverta.com.au) to connect the three downpipes on the south side of our house to the rainwater tanks. The advantage of using the Supadivertas is that we won't have to bother with any underground pipework.

I have concocted a very amateurish drawing of how I see the system working, though I am unsure whether this is actually feasible.





Our present round 2500L poly tank (which currently sits under our bedroom window) will be moved to a position next to (but not on) the easement, so that we can support it on a concrete base. We shall then place a rectangular Thintank to the right of it.
The dimensions of the present poly tank are as follows:

1250mm diameter
2195 height
2175mm present inlet height

The dimensions of the rectangular Thintank are:

1500mm length
75mm width
1950mm height

We have eaves and the approximate distance from the gutter to the ground at drainpipe A (the closest drainpipe to the tank) is 2.80m. The approximate distance from the gutter to the ground at drainpipe C (the furthest drainpipe from the tank) is 3.26m.

I have a couple of concerns at this stage -
1. Is drainpipe C, which is 17.34 metres from the rainwater tank, too far away? Will we get enough pressure in the pipes to fill the tank?

2. The pipes from drainpipe A and B will need to cross the footpath at some point and this will no doubt create a tripping hazard. This means we will have to ask for a groove in the paving before it is laid down to accommodate the pipe, so we had better know exactly where we want it, or is there some way of covering the pipe???

The current poly rainwater tank has been disconnected from the stormwater system and is now standing empty, so it won't be difficult to move it. It is partly buried in the ground though and I can post a picture of it but its height won't be a true indication of its height when moved.

Using Supadivertas has many advantages, one of those being not having the stormwater pipes annexed and used as a wet system with a vertical riser as per your original water tank plumbing. It is certainly an advantage that your stormwater system has been restored.

First Thoughts:

TANKS:
Having two tanks allows you to have a settling system whereby water transfers to the round tank and decanted water is transferred to the thin tank several days later. The transfer (balance) valves need only be 25mm and flexible hose used as the transfer pipe.

The pump would draw water from a 25mm valve fitted about 100mm above the bottom of the ThinTank.

Because the Supadiverta diverts water to a valve (low restriction inlet) fitted about 100mm above the bottom of the tank, you have the choice to not need overflow pipes fitted to the tanks. This (usually) also increases a tank’s storage capacity.

ThinTank. Height 1.950 metres.

You will gain additional storage capacity by capping or simply not optioning an overflow outlet but water must not cover the tank’s top inlet basket’s mesh. Having a bird bath is not a good design feature!

The tank will need to be optioned with two 25mm ball valves fitted 100mm above the bottom of the tank at the valve’s lowest point. Note that most tank outlets take the height from the middle of the hole but it isn’t a problem if they do this because the tanks will have minimal sediment when compared to standard rainwater harvesting systems.

Original round tank. Height 2.195 metres.

This tank has an overflow provision previously used at the top of the tank next to the inlet basket. This is bad design as its height does not provide any mitigation during heavy rain but the overflow opening can now be capped because the Supadiverta can also serve as the overflow.

Because this tank will be linked to the ThinTank, its full water level must be no higher than the ThinTank’s full level if the balance valves are left open during rain periods. There is about 150mm height above the top of the side wall to the top of the protruding inlet. This means that this tank can only fill to about 100mm below the top of its side wall to match the thin tank’s maximum capacity height but this will be compensated somewhat by the thin tank gaining about 100mm more storage depth.

The tank will require one 25mm (balance) valve and a 50mm valve, both fitted about 100mm above the bottom of the tank’s floor at the valve’s lowest level. Fitting ball valves is recommended.

Fitting Supadivertas.

Downpipe adaptors are required to couple the 90mm downpipes to the Supadivertas.

How much gap is there between the downpipe where the tank use to be and the small wall? The Supadiverta is 315mm long at its widest point but the length includes the downpipe.

When a Supadiverta is also used to substitutes as the tank’s overflow, the tank’s water level is governed by the height of the Supadiverta’s internal reservoir wall after the Supadiverta has been fitted to a downpipe. Once the tank fills to the same level, excess water will overflow over the reservoir wall to the stormwater system. There is a website address on the outer walls that is the same height as the top of the reservoir wall, this can be used with a laser level or a straight edge as line of sight.

The pipework doesn’t have to be connected at the same time the Supadiverta is fitted because wrapping some cling wrap around the internal filter will divert all water to the still intact stormwater system.

Concrete path.

It would be best if a common pipe serving DPs A & B is plumbed under the path. Because Supadiverta has a syphonic drainage system, it uses smaller pipes and this makes the excavation a lot easier. I anticipate the pipe being 40mm.

IMPORTANT: A pipe can dip down (under the path) then up again but it cannot be plumbed upwards and down again (as per an inverted U) as doing this will result in an air pocket.

If you Google “laying a pipe under a path” on YouTube, several videos will come up showing how to do a hydraulic excavation using a garden hose. The video below uses a pvc pressure pipe (American Schedule 40 pipe) to excavate the passage and another smaller pipe later plumbed but you will be using just the one pipe. If the end gets damaged at all, the last few cm is easily removed.

https://www.youtube.com/watch?v=KKTvln1lKBA

Plumbers know the above method and you will need a plumber to fit the Supadivertas to the downpipes which is quick and easy.

https://www.supadiverta.com.au/fitting.html

The plumber only needs to measure from the nearest Supadiverta because the other two Supadiverta's line of sight can be measured from the weatherboards.

Pipe sizes.

IMPORTANT: The pipes must not be oversized as having a regular adequate sediment flushing velocity is very important when having a wet system.

The big failing with standard wet systems is their annexing of the stormwater system pipes which must be compliant for a 1:100 year storm event as they also accept surface drainage and water from silt pits that ag pipes drain to.

They are also required to have a slope and to drain with channel flow whereas a rainwater harvesting wet system has pipes that flow full of water.

A stormwater pipe’s full flow velocity at the head of a wet system is substantially less than the minimum flushing requirement even during high intensity rainfalls, the reason why sludge builds up.

Unnecessarily large subsurface pipes also retain much more water between rain events.

Pvc pressure pipes are used and their sizes are determined by the region’s 1:20 year rainfall intensity, the region’s weather patterns, the roof areas servicing each downpipe and the tank sizes.

Melbourne has a minimum 1:20 year rain intensity of 2.2mm (rounded up) average over a five minute duration but about 95% off all precipitation is either drizzle or showers. The long term average for annual heavy rain events is five per annum.

I don’t know the roof areas servicing each downpipe but your total tank storage capacity will be about 4,400 litres.

Because a Supadiverta diverts water to a bottom valve, its hydraulic head is governed by the tank’s water level, not by the height of a vertical riser above the tank. More hydraulic head = efficient flow rates with the use of smaller pipes.

It must be noted that it requires x4 the hydraulic head to double the flow rate, the reason why a small hydraulic head is still surprisingly efficient when a tank is nearly full but to maximise efficiency, 45 degree wye fittings should be used in preference to 90 degree tees to minimise friction losses.

DP(a) I would use 20mm (23.7mm ID) pressure pipe vertical drops that merge to a single Class 9 25mm (30.5mm ID) pressure pipe. This pipe would merge to a 40mm 45 degree wye that also merges with a 25mm pressure pipe from DP(B). The 40mm pipe would be diverted under the path.

DP(C) I would also use a Class 9 25mm pressure pipe to divert water from this downpipe to ensure an adequate and regular flushing velocity. The pipe would merge to a 50mm pressure pipe wye that will also merge with the 40mm pipe.
The short 40mm pipe will have minimal friction/pressure loss and will recharge the DP(C) 25mm pipe’s friction losses as it will act as would a water tower.

The 50mm pipe will use a flexible UV stabilised hose to connect to the 50mm valve

Sediment trap. A simple sediment trap that would capture bed load would be best fitted near the round tank. The Supadiverta has an internal 750 micron filter on a 50 degree slope but a surprising amount of fine grit and other matter still finds its way into the wet system pipes. The sediment trap collects this and flushing entails minimum water loss.