Rainwater tank buyers guide

There’s more to a rainwater collection system than just installing a tank. Lance Turner looks at what you need to consider when installing a system, what tanks are available and accessories to improve the operation of your system.

Rainwater tanks come in almost any size, shape and colour you can imagine, with a variety of materials to suit different preferences or usage requirements. So what should you look for when buying a tank, and what other components are required to make the system operate reliably and hassle-free? We consider siting, size, installation, tank materials, water collection, water use and more!

Selecting the site, size and shape

The first decision you have to make is where the tank will be located. Where you place the tank will determine its size and shape, and possibly even its colour if it needs to blend into the surrounding vegetation or walls.

You may want to place the tank next to the house or shed, which makes water collection simpler and reduces pipe runs. If the tank needs to be placed away from the house, the plumbing will be more extensive, complex and expensive. Access to power is also a requirement if you intend to include a pump in your rainwater system.

Accessibility for maintenance is also important. You may need to be able to clean behind the tank to remove leaves and debris, and any filters or first-flush diverters at the tank will need occasional cleaning.

If there is to be a pump and other equipment, it’s usually best to locate them close to the tank if possible, so allow for this. Alternatively, you may just have a simple tap on the tank for filling watering cans or to feed a slow drip irrigation system, allowing gravity to do the work. The higher the tank in relation to the point of use, the better the water pressure, so consider this if you are going to go without a pump.

In hotter climates, it’s preferable to place the tank in the shade if possible, to reduce tank water temperatures and hence evaporation, as well as possible bacterial growth. If you can’t find a shady spot, make one by planting a fast-growing bush on the sunny side of the tank—there are some excellent Australian native shrubs that grow quickly and are excellent shade plants—check with your local nursery for appropriate plants.

For most city dwellers, space is at a premium, so the size and shape of the tank is usually determined by the space available. If space allows you to install any size of tank you wish, then it should be sized according to your water needs from it, the roof collection area and your location’s expected average yearly rainfall. This sounds complicated, but fortunately the hard work has been done for you in Renew’s Tankulator rainwater tank sizing calculator. Check it out at renew.org.au/tankulator before you decide on your tank capacity.

For high-density living or where above-ground space limits you to a tank smaller than you’d like, an underground tank may be the solution. These are available as poly tanks or concrete, the latter often cast in-situ. Concrete tanks are usually reinforced internally and as such can support heavy loads, so they can be placed under driveways. Some underground poly tanks are also well reinforced and can withstand considerable loads. Undergound tanks are usually best installed as part of a new build, but are also suitable when doing major ground works, such as replacing a driveway or laying a slab for a garage.

If your house is mounted on stumps, or you have a post-mounted deck, you could consider a bladder tank. These consist of a metal frame around a flexible plastic or rubber bladder. As the bladder fills it expands to its maximum size. However, periodic washout maintenance (if required) of a bladder tank poses more challenges than a tank which enables internal access.

You also need to consider how the water will get from the roof into the tank. If you locate the tank away from the collection gutters, you may need to use what’s called a ‘wet’ system, which can add to costs and complexity. See ‘Wet vs dry systems’ later for more on this.

Download the table of rainwater tank suppliers here to help you find the right tank for your needs.

For the full tank buyers guide article, purchase Renew 145.

About the author
Lance Turner is Technical Editor of Renew magazine.
This article was first published in Issue 145 (Oct-Dec 2018) of Renew magazine. Issue 145 has saving water as its focus.
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