The best size for your home depends on how you plan to use your saved rainwater. Don’t worry about whether there’s enough rain to fill your tank – often the bigger problem is disposing of the excess water!


Five Main Uses for Your Rainwater Tank

  1. Prevent flooding by controlling the flow of water during heavy rain
  2. Save rainwater for the garden
  3. Save rainwater for drinking
  4. Use tank water to reduce your scheme water consumption inside the home
  5. Replace your use of mains water completely

These are listed below in order of increasing demand for water, tank size and cost.

1. Prevention of flooding by controlling the flow of water

Best size of tank

  • Many homes unfortunately have issues during heavy rain with water pouring out of downpipes and flooding over paths or overflowing out of soakwells that are too small. 

• A rainwater tank can be used to hold the surge of water temporarily and then slowly release it into a soakwell or sub-surface drain where it can be absorbed by the soil.

• A valve at the base of the tank is used to control the rate at which it empties. At the end of the winter, closing the valve allows the tank to fill up and store water for use in the summer

For a small gutter spout draining a small area of roof or acting as a gutter overflow a small tank of 720L to 1500L is adequate. For one or maybe two downpipes carrying a lot of water a 3000L tank will work better. If you want to store more water for use into the summer then opt for a larger size tank -ideally 10,000L or more

2. Save rainwater to irrigate the garden with a bucket or hose

Best size of tank

  • Connecting a raintank to a downpipe from your gutter to store water for your garden is the simplest option. But when it rains and the tank fills isn’t generally the time of year that you need to water your plants. So your rainwater tank will be overflowing for several months and then quickly emptied.

• Whilst using a rainwater tank solely to water the garden is the lowest cost option, it’s also the least efficient in terms of cost recovery and maximizing usage.

As large as possible. Cost per litre of water stored falls quickly as tanks get larger. Your options range from 300L up to 3000L in a slimline plastic tank (sometimes called an ‘undereaves tank’), up to 7600L in a corrugated steel slimline tank or up to 250kL in a round tank

3. Store rainwater for drinking

Best size of tank

  • Many people prefer the taste of rainwater over scheme water. The Health Department does recommend mains water as the safest for drinking water because in the city you’ll otherwise miss out on the effects of fluoridation.

• A filter jug can be used to remove any sediment. An external or undersink cartridge filter is useful, but will need a pump to provide sufficient pressure to force the water through

500L to 1500L is adequate for most households

4. Use tank water to reduce mains water use inside the home

Best size of tank

• An increasing number of new homes have the facility to connect the laundry and toilets to a rainwater tank . Using tank water to replace mains (scheme) water use through winter & spring will on average cut your total mains water use by 10-15% per year. Minimum 3000L
• But you can also supply your hot water system, and as that uses at least as much water as your washer and loo combined your annual savings could be increased to around 1/3 of total use. Around 5000L-6000L for a family home with adequate catchment area. Cost-effectiveness falls as the tank gets larger than this
• Want to plumb rainwater into an existing house? It’s relatively straightforward with an old house where the pipes run along the outside of the house, but is more effort when they’re up in the ceiling. We can advise on how practical it would be.  

5. Replace mains water use inside your home

Best size of tank

• If you’re not on scheme water then an average household needs a water tank of minimum size 90kL just to provide water all-year inside the home. You’ll need to harvest water off your entire roof too.

• We have experience in designing and building these large systems for rural homes – ask us for more details.

A higher capacity tank of 130-160kL isn’t much larger on the ground, or much more expensive, and will provide a reserve for dry years.

If you’re reliant on them , having tanks is always safer than one!

In general, look for the largest water tank that fits your space and budget. Larger tanks are not only more efficient but more cost-effective too. And round tanks are cheaper if you have the room to fit it into your garden.

See the Options Available  page for our full range of sizes and shapes


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