Installing A Water Tank And Are Rainwater Tanks Worth It.

A few years ago Brisbane was going through a mild drought. I say mild because realistically it was just water restrictions and the introduction of pay per use water. I’ve seen what real droughts do to rural areas and having to wash your car using a bucket and no longer being able to use sprinklers was hardly devastating to our lives. With the restrictions on water use came a wave of water tank sales buoyed with a govt rebate scheme in 2008. It is amazing how many people jumped onto that bandwagon without really thinking about it. Free govt money! The cost of a tank today is pretty much the same price as the cost (after rebates) back then, so I’m guessing tank installers were taking the rebate as cream.

At the time I thought it might be a good opportunity to get one so I checked out pricing and crunched some numbers. I based it on a 3000L tank as it would be the only size I could realistically manhandle down my hill and it was the minimum size required to get the rebate. (There were other stipulations as well such as getting it plumbed to your laundry or toilet which added extra costs not to mention the large costs of concrete/gravel or sand base)

The price of water was around $1.20/1000L so a full 3000L water tank had around $3.50 of water in it. I think at the time my out of pocket costs would have been $800 for supply only then the cost of me creating a bed for it etc. So based on that I would need to drain a full tank 228 times to recoup costs. In a perfect world of raining once a week and using the full tank over the remaining 6 days it would still take nearly four and half years to get the money back.

That may not seem so bad but the reality is Brisbane has around 110days per year average rainfall, most of which pummels down for weeks on end and then during autumn and winter we have 2-3 months of absolute dry. So during the 3 month rainy season you have no need to use your tank, then your tank remains empty sporadically for the remainder of the year. So even at optimal use you’re looking at a decade to get your money back. So back then I decided it wasn’t worth it.

From an economic standpoint, unless you experience water shortages, have costly water bills or the town supplied water is full of chemicals, then don’t bother. Your town supply water is essentially a giant water tank (usually a dam or natural waterway) accessible by everyone. From a permacultural perspective you do want it as harvesting and trapping the energy of that water on high ground is a valuable resource. Plus plants seem to do better when fed rainwater over town water, at least here in Brisbane.

Which leads me onto the next part.


It may seem silly but not many people know how to get the best use of their water tank. There are hundreds of thousands of suburban households who hold onto their precious tank water and then when the rain comes it’s still full so every new drop gets wasted via the overflow!
The first few days of dry after a rainfall start using your tank. Top up your pool, make compost tea (best water for it) and water your garden. So unless you rely on your tank for survival, you want it drained dry so that when the next rainfall comes, your tank is able to collect the maximum amount of fresh new rainwater.


Gravity is your friend, use it. Put your water tank at the highest convenient spot on your property. An ideal setup is to work out the height of your tank. Then find a spot where the top of your tank is just below the downspout of your gutter. This is the highest point your tank can sit and still fill up from the roofline.

By doing this you trap the water in a high potential energy position. This can allow you to negate the use of mechanical pumps. Your food forest is planted below the tank all the way down to the lowest point of your land. By digging swales on contour you can further trap tank overflow water and create new subterranean water basins that retain moisture in your soil and feed your plants.


I got my 3000L tank off a friend who was getting rid of his. I did a contra deal where I took off the price of a $280 UPS from some tech work I was doing on his business’ voip system. Two of us dragged it onto a friend’s truck which had a tail lift. Once at my place we slid it down the bank on the side of my house using ropes to control it and there it lay for a long time while I got around to creating a flat spot for it to sit.

I figured the best spot would be directly under my deck to the side of the house. This would be high enough for me to gravity feed to the yard and close enough to minimise piping to the tank. It took 3 days of digging to get it relatively flat, a lot of which was cutting through numerous giant roots from a Chinese Elm. Then another day of digging the 600-800mm deep holes. Clay and shale do not make for fun times.


I was driving along when I saw a heap of renovation rubble in someone’s front yard. I knocked and asked if I could fossick and they said yes. I did about three trips and couldn’t believe these amazing hardwood sleepers were going to be sent to landfill. They were all odd length pieces but nothing a bit of planning on some paper couldn’t sort out. First thing was to screwed a piece of wood to a star picket and then clamp the uprights to it to keep them in place.


To minimise the digging I’d have to do I did a shared hole in the corner. This also reduced the amount of concrete I had to use. The recycled hardwood sleepers already had notches in them so I positioned them such that I could slot the retaining sleepers into the notch and keep it in place as additional structure.


The black coating on the sleepers is ‘Diggers Eco In-Ground Timber Protecta’. It’s basically a bitumen coating so ‘Eco’ is stretching it in terms of marketing. It’s supposed to be the replacement for creosote which is no longer sold. I figured that I’d got the sleepers for free so may as well give it a bit of help to last longer, especially given that it’s holding up over three tonne of water, tank and concrete bedding.


Once bolted in place it was time to backfill.


With the help of a friend we mixed up and laid the concrete bed. I used a lot more concrete than I had planned but it’s rock solid. I opted not to cut the uprights to ground level. They act as a secondary barrier preventing any tank sliding and I really couldn’t see any immediate use for such short pieces. I may use them in their current position in the future for some sort of trellis framework. You can also see how steep my block of land is up to the road. My deck is 5m above where I’m standing taking the photo and the road 7m up.


Using some ropes tied off to the mulberry tree stump halfway up the hill, three of us managed to drag the tank uphill, flip it around so the overflow and lower tank outlet were facing downhill and lift it onto the pad. Unfortunately all the greenery shooting up in the photo is from that Chinese Elm I mentioned before.


A friend gave me a bag of 1″ ball valves and fittings from his work that normally get thrown away after each job. Other than a thin bit of concrete on the outside of them there’s nothing wrong with them. Recycled industrial garbage saved me a further $30.


The side outlet required a 90º elbow to get around the post and the hose came with the tank. The side outlet sits about 30cm above the front outlet.


Then it was time to plumb it in.