Rain Water Harvesting & Fire Fighting Water Tank

Our block of land is BAL rated. As part of our DA approval, we need to install a 10,000L minimum tank made out of non combustible material for fire fighting purposes. I am a keen gardener, and can appreciate how valuable water can be especially during summer, so I don't mind going through the trouble to have a good rain water harvesting system put in place. I would be happy to put in 20,000L or even more. There is already a 6000L tank next to the house that will flush the toilet and do the cold cycle for the wash machine.

I am quite annoyed by my builder who is a project home builder. They just want to press GO and don't really care about a good solution. They strongly suggested an above the ground tank that is stand alone and that doesn't even take water from the downpipes. I have to push back on this and tell them I am happy to pay extra to get something that has our best long term interest at heart. I don't even know if they have the expertise to do it properly. The hydraulic engineer they subcontract their work to doesn't want to talk to me on the phone (my customer service rep asked me to talk to him directly). His answers to my email questions are brief and cryptic. Long stories short, I thought I should do as much research and learning as I can even though I am totally out of my depth on this topic. Hence this long post.

I have a few questions:

1. What's the best location for the tank? The water access needs to be within 4m of a fire truck. So the tank can either be located at the front of the block near the driveway, or there needs to be an outlet near the driveway for the fire truck (I suppose we need to run an underground pipe to get the water over to the driveway if the tank is located far away from the driveway). I've attached a sketch here and marked two locations (A & B) at the front of the block where I thought makes the most sense. Very open to any other ideas.
2. What tanks are the most suitable? Above the ground tanks at this capacity will be huge, even though we have the space for it, and can probably camouflage it through landscaping, I am still hesitate about using above the ground tanks. I'd rather use the space for gardens than tanks. I know underground tanks are a bit more expensive and I can accept that difference. But I don't know how much more it will be in terms of total cost, excavation, maintenance etc. Could any of you share some insight please? Is the quality of underground tanks good? What happens if something goes wrong? Does it need to be maintained and serviced/cleaned regularly?
3. I've just heard that there are retaining wall tanks (basically, the retaining walls are hollow), how reliable are they? Would they topple over if the inside is dry? We will have retaining walls during the landscaping stage, do I need to get the design and pipes sorted now to accommodate this later?
4. We could also put tanks under a new deck (the deck can only be built after the house is built) as our land has a slope. Do I need to consider these in the hydraulic design now? Do I need to put the pipes in now?
5. There is an existing 10,000L plastic tank at the rear of the block (marked with a pink circle), presumably it was connected to the old house (before it was demolished and land subdivided). I am keen to use this tank as well if it can be done without too much trouble. Checked out this tank a few days ago, there are pipes going in and coming out. It seems the pipes going out just releases water on the surface (I guess that's the overflow). There isn't a storm water drain near the old tank. Is it worthwhile to reuse this tank? Is there another way to manage the overflow?
6. If we manage to get 20,000L minimum, ideally underground tank, can we / should we get rid of the 2x3000L slimline tanks on the side of the house? This way, that area will look neater, and I will have more space. If the new large tank is further away from the house, would that cause a problem if we want to use the water for flushing the toilets?

Thanking you for your time and I am really looking forward to your advice.

I assume that you are on the water grid. Yes/no?

Hi SaveH2O, yes we are on the water grid (suburban Sydney). I know from past experience that water will be a problem even for a very small garden if you only have a small water tank. The new garden will be bigger and I want to grow some vegetables and fruits too. I can't bring myself to using town water to water the garden hence I'd like a more sustainable way to keep the garden hydrated during the dryer months.

It sounds like the builder is suggesting having a 10,000 L fire tank as permenant storage in the most suitable position. This makes sense as it would either fill remotely if you had the correct set up and hydraulic head or else have 10,000 L carted in.

It is best if you ask the local CFA this question. They will appreciate it.

Most hydraulic engineers are pretty useless in this field. You will find numerous mistakes with hydraulic designs posted on Homeone that I have answered over the years. Trouble is that they keep making the same mistakes time and again. All text book, no understanding!

Underground tanks are a bit more than a "bit more" expensive plus an above ground tank is easily seen and more accessible. You could however include this topic in your discussion with the CFA.

Go to the Landscape Tanks website. https://www.landscapetanks.com.au/

They are a good idea and certainly add ambience and value to a property. I strongly suggest that you talk to them. I did an expo several years ago at Mornington Racecourse, Landscape Tanks were opposite me and I spent time examining the display and talking to the person on site. I was impressed.

If you are thinking of bladder tanks, I am not a fan because they often turn putrid due to their lack of an air/water interface. There are however small modular tanks sold and also squat tanks that could be suitable for the area.

You basically have two choices of rainwater diversion...
1. Divert the downpipes as wet systems which means incorporating the tanks (including Landscape Tanks) into the stormwater system and...
2. A system that leaves the stormwater system intact by diverting water, not downpipes. I know a bit about this type of system because I researched and developed the Supadiverta. Read through the recent Homeone thread linked below.
viewtopic.php?f=35&t=97686
This can be fitted at any time and you don't need a plumber. You can also opt not to have an overflow pipe which also means that you can harvest as many downpipes as you like without fear of the tank(s) ever overtopping.

The primary considerationfor both systems is the land slope and the available hydraulic head between the house and the tank which obviously dictates the tank's height.

A problem with remote located tanks is often an overflow that is expensive or too troublesome to divert back to stormwater and your tank solves this issue by discharging to ground. Does this discharge cause problems?

If you can reuse the tank, then sure, go for it. Is there a pump connected? I assume not.

It would also be a good idea to rig up a syphon hose to slowly run over the bottom of the tank because there is bound to be a decent sediment layer by now.

I take it that there is a pipe rising up the side of the tank and this pipe discharges water to the tank's top meshed inlet. The pipe rising up the side is called a vertical riser and these invariably don't have enough velocity even during the heaviest rains to flush out the sub surface horizontal pipe unless there is a flush valve fitted to the wet system's lowest point. Do you have a flush valve?

A wet system should also have leaf diverters fitted to the downpipes to prevent organic and other matter from entering the pipe and also prevent mosquitoes from accessing the standing water. From egg to adult mosquito takes between 10 to 14 days. Do you have leaf diverters on any downpipes?

Are the slimline tanks connected to toilets and laundry?

If you already have the tanks, pump and mains water change over device already in use, it would be a shame to disrupt it but the system will most probably still need some modification because very, very few rainwater harvesting systems are not sub standard. If you post a few photos of the tanks, infeed pipes and pump etc, I can give an informed opinion. Is the pump submersible or external?

IF you are able to remotely (or permanently) connect a remote tank (or two) to recharge the house tanks, it would be great. Do the site levels allow this?

Plenty of people have remote located tanks and a good jet pump (they sacrifice some pumping efficiency for better suction performance) will have no trouble drawing water to the house through a decent internal diameter hose. It must be remembered that toilet cisterns and washing machines are low flow end fixtures that don't need a big pump.....which most people are sold but that's another story.

Hi SaveH2O,

Thank you very much for the very detailed and considered reply. There is a lot of useful information to digest and your reply is good food for thought and generated more questions from me. I've followed the order of your post below.

For the above the ground tank, what do you mean by 'fill remotely', do you mean connecting the tank and the downpipes underground and simply place the tank in the most suitable position? Or does that mean using a hose and a pump to transfer water from one location to the other? The biggest problem I can see with this an above-the-ground tank is aesthetics. The most suitable position will be front of the house, and a 10,000L tank is very large. It will be a big turn off for prospective buyers years down the track when we decide to sell the house in our old age. The builder suggested an above the ground tank with water carted in - this definitely is the easiest, quickest and most economical solution, except I don't think this is the best solution.

The NSW equivalent of CFA is RFS (Rural Fire Service) and I am meeting them onsite in a couple of days, they will confirm the best location for me. One big question is whether I can have a couple of large tanks (say 20,000L) located under the deck at the rear of the house, and send an underground pipe to the front of the house, attach a suitable outlet for the fire truck to use. If this is doable, this would be my best solution - tanks are out of sight yet still above the ground therefore economical and easy to maintain, with this volume, I would have plenty to use for gardening and plenty leftover for firefighting. If this is doable, what fixtures do I need? The block of land slopes down from the front to the back, so I suppose I would need a pump to send the water from the back (lower) to the front (higher)? The other problem is we don't have the deck yet, therefore I don't know exactly what volume of water I can hold under the deck (it is a vacant block at the moment, with some trees and shrubs).

I have made contact with landscape tanks and visited a couple of houses which use their tanks as front fence. I will order a couple from them, to be used on one side of the house instead of a retaining wall. There is also another supplier called tankwalls.com.au, similar concept and products, do you happen to know them? In your opinion, which products are more superior? The landscape tanks can only go in after the house is built, so the builder has told me they will provide a connection from my basix tank for overflow to be provided to a T junction where I can then connect to the future landscape tanks. Does this sound like a good solution? Do I need to clarify anything with them? I will post a picture with the locations of all tanks (existing and proposed) marked tomorrow - everybody is asleep now and the printer/scanner is in the bedroom.

Not considering bladder tanks based on your take.

Very interested in your supadiverta. As we are in a bushfire prone area, I gather we probably have metal downpipes, does the supadiverta also comes in metal?

I read through the post you mentioned where someone who is quite handy is doing the system by himself. I have to say a lot of it went over my head.

With the existing water tank (empty since the old house was demolished) that is currently discharging to ground, I assume it wasn't a problem before (it was an old house, so water discharging rules may have been different). Where it discharges is near the boundary with very little human traffic, and from there it goes downhill to a heavily wooded valley and there is a creek at the bottom of the valley. If we eventually reconnect this tank to the rain water harvesting system, I imagine we can leave the discharging the same? We could use this as the last tank to fill (fill the under-the-deck tanks first then this one) so the discharge is minimal. Not sure if there is a pump connected, I don't know what a pump looks like. I have no idea if the existing tank have a flush valve or not, I haven't paid much attention to it. I shall have a look at it next time I visit.

Slimtanks. Yes the new slimline tanks are connected to the toilets and laundry. When there is no water left in the tank it will switch to town water. 6000L sounds like a lot of water if we only use it for toilets and laundry. The builder told me we will use tank water only if we are doing a cold wash in the laundry. If we are doing a warm or hot wash, then it would be town water. I am fine with that. I've always wondered if the tank water is clean enough to wash the laundry as we have two little ones. How do you ensure the water is as clean as possible in this setting? Because nothing is built yet so I can't give you any photos of the tanks, indeed pipes or pumps. What questions should I ask the builder to ensure I have everything that is necessary for this system to work efficiently?

The roof area of the new house is about 200sqm and our post code is 2076, I think there is more than enough rain water to feed whatever tanks we may end up with.

Thank you for your time.

I was just about to tag you into this thread, now I don't have to, you're already here.
Very tidy work!

I had assumed that there was an existing house. So...it is a new build.

"Fill remotely" means that there is no pipe plumbed to a tank and so it can only be filled by transferring water (usually by gravity feed) via a long hose (usually poly pipe) from another tank or diverted from a downpipe diverter that facilitates a remote application.

If a tank is only used to hold the required emergency rainwater storage for fire fighting, plumbing a pipe and having to consider an overflow is usually unnecessary extra work if the tank must always remain full but the judgement on what to do can't be made by someone (like me) not on site.

Not all tanks are ugly and you could have a feature framework partially around it on which to grow climbing roses or clematis etc.

The builder probably suggested having the tank sited in the RFS preferred spot and filled with carted water because that is what he is use to seeing and is the easiest.

The RFS are only concerned with access to water and so your pipe idea is good but the tank's base obviously has to be higher than the outlet. I understand that the Storz fitting isn't necessarily a standard 65mm in NSW but they will tell you their preferred size. You cannot rely on an electrical pump during a fire.

I don't know Tankwalls.

The Supadiverta is made from Acrylonitrile styrene acrylate (ASA) plastic and is not fire resistant. I suggested it as a possibility because they allow you to harvest numerous downpipes without having to worry about the tank ever overflowing plus it has a 750 micron filter but it most probably is not suited to your property. There are nevertheless lessons learned from the research, development and practical experience that can be applied to improving a standard wet system so as to deliver better quality water with higher yield at minimal additional cost. The two main featires to incorporate would be a sediment trap and a low restriction inlet. These are detailed in the thread previously linked and also further below.

If previously there was just the one tank, the wet system will almost certainly stil be connected. Is there a pipe (vertical riser) that rises up from the ground and terminates above the tank's top meshed inlet? If so, can to see a flush outlet anywhere that would drain the wet system when opened? What condition would you say this tank is in?

Re an overflow serving the Basix and Landscape tanks, the overflow capacity must be equal to or greater than the inflow capacity during a storm when the tanks are full to prevent overtopping. This unfortunately is an area that often fails because few of the persons who design and install systems know how to do the calculations. Before anything is plumbed, you need to examine their hydraulic calculations.

Clean tank water:

The basics is to have the best quality water possible delivered to the tank and the best quality water in the tank delivered to the pump. Simply stated but rarely done.

A wet system retains standing water to the level of the top of the vertical riser, for this reason the outlet that discharges into the tank and the downpipes should be mosquito proofed which also prevents organic and other matter entering the wet system. The only leaf diverter that I recommend is the ICON Leaf and Debris Controller which can be ordered through the Bunnings Special Orders desk. It costs about $38.

A simple DIY sediment trap using off the shelf parts will capture bed load and greatly reduce the amount of sediment build up in the tank. Flushing the trap discharges a fraction of the water that flushing a wet system does plus the water retained in the wet system is of much better quality.

We use an invert taper rather than a pipe reducer now. The smaller pipe has increased velocity and discharges less water. A cheaper tee can also be used as the leaf diverters will keep larger objects out of the wet system.

Water falling into a tank through a top meshed inlet results in sediment resuspension a lot of the time but this is greatly reduced if a low restriction inled is fitted to supplement the vertical riser. This is usually a 50mm inlet branched off the main pipe and fitted about 100mm - 200mm above the bottom of the tank. Advantages include:

1. By discharging lower than the vertical riser, it operates with greater head which gives it priority flow.
2. The inflowing oxygen rich water sweetens the high density anaerobic zone.
3. The inflowing water quickly de-energises inside the tank and being low density, rises to the top.
4. The external standing water will be at the level of the water in the tank, not the level at the top of the vertical riser.
5. The additional flow path increases the wet system's flow capacity.

If you have more than one tank, you should divert to a 'settling tank' that sends decanted water to the tank that supplies the pump.

The best quality water is found 150mm - 200mm below the surface yet most pumps draw water from the bottom anaerobic zone which is the worst quality water in the tank. Most irrigation shops will make a floating filter intake hose for you that will connect to a 'balance' outlet valve that sends decanted water from the settling tank to the tank supplying the pump. This is discussed in the link previously posted.

Don't have the outlet valve that supplies the pump fitted close to the bottom of the tank (which is commonly done), a minimum 100mm at the valve's lowest point should be the rule.

If you have a submersible pump that draws water into the bottom of the pump, make sure that they have it raised above the sediment layer. Most are just plonked onto the floor where they spend a shortened life vacuuming the tank's sediment layer.

You can also get hit hard ($$$) with the mains water switching device. I prefer the non powered (and bullet proof) hydraulic ones like the Acquasaver but many outlets now make cheaper ones that work the same way but at a much reduced cost.

http://www.acquasaver.com.au/

https://asctanks.com.au/product-categor ... over-pump/

If you are only supplying low flow end fixtures like cisterns and washing machines, you don't need a powerful pump.

At 20 lpm, a 12mm garden hose has about 8 time more friction loss than an 18mm garden hose. Attaching a short length of 12mm garden hose to an 18mm garden hose so that you gan use your standard 12mm garden fittings will allow a small pump to outperform a larger pump fitted with a 12mm hose.

If the pump also supplies a garden tap, use large hose/pipe between the pump and the tap to reduce friction losses.

An old thread that used settling tanks, leaf diverters, low restriction inlets and sediment traps had a 1 year summary which is linked below. Note that the system was designed specifically for the area's (QLD) rainfall pattern which is much different to SA.

viewtopic.php?p=1146540#p1146540

HI SaveH2O,

Thank you so much for spending so much time on my post. I've read the linked posts and like others I appreciate your input on my post and in this forum.



As mentioned in my previous post, here is an image of the house outline, as well as where the existing and proposed tanks are.

Tank A is an existing tank. I don't know how old it is but I can find out. Last time I looked, there were various tubes attached to it so it must have been used then disconnected when the old house was torn down. As far as I can see, the exposed tubes were capped to keep them clean. I couldn't see the top of the tank. I will try to take some photos tomorrow (the terrain is a bit rugged and the grasses are long, I am worried about snakes. I don't normally venture there unless someone can walk me to that section). I intend to recommission this tank if it is still in working order. I've asked the builder a few times about connecting this tank to the downpipes but I think it is too hard for them.

Tank B is where I think the dedicated fire fighting tank should be, it can be accessed most easily. I am meeting with RFS (Rural Fire Service) Community Engagement Officer onsite tomorrow so they will let me know if this is the case. I set my heart on an underground tank but I don't know how much it costs yet (the builder is costing it). I might change my mind after I see how much it costs. I originally asked for 2x10,000L underground tanks, but the builder is only pricing for 1, it makes me think maybe the cost for two is prohibitive.

Tank C will be two landscape tanks working as retaining walls as well. The builder doesn't deal with the supplier of the landscape tanks so we will need to install those after the house is built. The builder will provide a T junction at the end of the downpiple for me to connect to the landscape tanks down the track. I will get in touch with the landscape tanks supplier and confirm if this works. I don't quite understand your comment "the overflow serving the basix tanks and landscape tanks must be equal or greater than inflow", I can't figure out which tanks get filled first, let's say the two landscape tanks get filled first (they are lower) then the slimline basix tanks, I imagine the overflow will go to the stormwater drain (there is one nearby, and there is another one not far down, and I think that will eventually go to the creek at the bottom of the valley - our boundary is in the middle of the creek). Does this mean there is almost infinite overflow capacity?

Tank D is something I want to do, but won't be able to do until after the house is built and after the deck is built. the block naturally slopes from front to back, so there will be a drop of about 800mm (it is hard for me to figure out at the moment because the builder will cut and fill to build the house and the house will sit higher than the levels indicated on the plan but I don't know how much higher. I will try to find out from the builder). If the drop turns out to be only 800mm, I am not sure I can find a squat tank to fit under the deck. I was thinking about the possibility of using some of these tanks as the firefighting tank by pumping the water up to where Tank B is (and wouldn't need Tank B anymore) but inability to use a pump rules this out.

Your comment about installing a leaf diverter, a sediment trap and a low restriction inlet is good advice. Are these best done by the builder or can I do it later after handover? The builder wouldn't use anything that is outside their supplier network, so I have to install the ICON Leaf and Debris Controller after the house is built.

Thank you again for being so generous with your time and knowledge. I must admit I don't understand everything you say, I have to read multiple times and I am certain I will have more questions.

If you post a photo of the pipes you see at the tank, I will be able to give my opinion as to what they are.

If the builder was to reconnect to the tank, they almost certainly would want to lay their own wet system pipe.

There is a decent slope to the tank and an overflow pipe unfortunately cannot flow uphill. The builder may also be concerned about the legality of the overflow discharging to ground but as long as the overflow doesn't impact on a neighbouring property, it will be fine.

How did your meeting with the RFS go? What was their opinion about an underground tank?

Underground tanks are expensive plus hooking up a Storz fitting to one would prove let's say 'interesting'.

A common issue with water tanks is having an overflow outlet that has less discharge capacity than the inflow capacity during heavy rain. One way to safeguard against this is to not have a flow restricting meshed overflow outlet that are also prone to blocking. This can be achieved by having either a flap valve or an air gap that is fitted with mosquito proof mesh in the vertical section.

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

https://www.rainharvest.com/rain-harves ... taag99.asp


The mosquito proof overflow mesh will typically have an open area of about 53%.

The tank's overflow rate at different heights above the invert must still be calculated (or known) so as to know the maximum inflow rate which must be less than the tank's overflow capacity. It is a widespread industry failing that tank manufacturers and plumbers don't know what they should know.

Leaf diverters are essential for wet systems but most are poorly designed and don't even consider having a once popular basket type.

The low restriction inlet only requires an additional inlet about 100mm above the bottom of the tank and this can be optioned. 40mm or 50mm are usually chosen. It only requires a flexible coupling fitted to a ball valve (hard connections are never recommended due to ground movement) but the wet system pipe ideally needs to be DWV, not stormwater. It is very easy and quick to plumb. The H1 thread installation I posted previously has one plus a sediment trap.

The sediment trap only uses a few off the shelf pvc fittings but it is much easier if it is plumbed when the wet system pipe is laid. It is well worth doing because it prevents the sub surface pipe building up muck (the bane of wet systems), improves the water quality and the tank will have much less sediment. It is quick to do and I can't see a problem with the plumber fitting a few additional standard DWV fittings.

HI SaveH2O,

I want to ask you about a couple of quotes I've received from the builder.

Are gutter and leaf guards important? They were not included in their original price. When I asked for a quote, they quoted nearly $9000. I don't know how much these things cost but $9000 sounds like a lot. Is it a reasonable price or am I taken for a ride?

The quote for the underground plumbed in 10,000L tank came in at more than $23k. I knew this was going to be expensive but does this sound reasonable? I can send you a breakdown if that helps. I am now inclined to just do an above-the-ground tank with static supply (not plumbed in).

TIA.

A builder will use someone they know plus add on their usual 20% for something that you can have done post build.

Unless you have a significant leaf and debris blockage problem, I would steer clear of gutter guard for the following reasons:

Half round gutters have superior flow and flushing characteristics. If you want the best performing gutter, these are the way to go.

Gutter guard is effectively a very low angled filter.....not a good design choice!

The gutter guard with small holes is prone to trapping small organic matter such as tiny flowers and is high maintenance. Been there...done that!

Gutter guard disrupts the natural fall of water off the roof which has a back flushing effect during initial heavy rain. This causes a greater amount of sediment to build up. Organic sediment build up promotes rusting in metal gutters due to metal atoms becoming positively charged when ionisation causes their atoms to lose their electron whereas organic sediment is negatively charged.

Gutter guard requires maintenance and should be fitted with easily removable access sections but this design necessity is a rarity.

Having to climb a ladder to remove gutter mesh can be dangerous. I once had to remove LeafBusters mesh by climbing a ladder on the steep side of the house and removing screws holding down an alloy strip on the gutter edge only to find that it was also siliconed to the gutter edge. After I had finished with the cleaning maintenance, I had to replace it all and that was only the first section.

If you have a rainwater harvesting system, you should have leaf diverters fitted to the top of every harvested downpipe to not only prevent muck building up in the underground wet system pipes but to also to prevent mosquitoes and other pests from accessing the standing water. It is mandated in most northern regions for mosquito proof leaf diverters to be fitted to all downpipes serving a wet (charged) rainwater collection system but it should be mandated everywhere.

The ICON Leaf and Debris Controller (what a mouthful) can be ordered at the Bunnings special orders desk because Bunnings deal with Icon Plastics. They cost $38 each and can be fitted post build.


I warned you! Save your money.

The quote will also include the builder's margin.

There is a lot more work involved when plumbing an underground tank plus the tank itself is invariably more expensive. There is also the overflow consideration.

Just have a tank that you can fill remotely when first and later needed and don't worry about the overflow plumbing if you do this.

Thanks SaveH2O, I know I can rely on you for a good explanation and sound decision making. Very much appreciated!

Hello Huggies. We are in the gutter guard and gutter cleaning business ourselves. Another option for better water flow is just having extra downpipes. But if you do decide with gutter guard and want a cheaper option that is easier to remove when its needed check out our Triple-G system! https://graysonsgutterguard.com.au/gutter-guard-install/