Water tanks have four main uses:

  • Water for the garden – water to do plant watering with, this will conserve water and save you needing to use mains water
  • Water for drinking – rain water if stored in the correct tank is quite suitable for drinking
  • Water for washing – you can easily use this water for washing your clothes in
  • Water for flushing the toilet – perfect for the job!

What can I use a rainwater tank for?

Rainwater tanks should NOT be used as a means of supplying drinking water in urban areas due to traffic and industry emissions that can settle on roofs.

In order to get good use out of a rainwater tank and maximise its value, you should consider connecting it for indoor usage. In this way you can use the tank all year round and particularly during the winter months when outdoor use is at a minimum.

Garden watering

The percentage of household water use in the garden varies from less than 25% to more than 50% across New Zealand, generally depending on a household’s geographic location.

Larger rain water tanks tend to be more beneficial as you can store a large amount of water from the wetter seasons to use in your garden through dry periods.

Toilet flushing

A toilet can use up to 12L per flush so installing a tank to toilet system can lead to major water savings. An average person uses 30L of water in the toilet per day or 210L per week.

You can install an automatic diversion directly from mains water if the rainwater tank is empty. Alternatively, a trickle top up system uses a float valve to measure how much water you have in your tank. When the water level gets too low, mains water will trickle into the tank to top it up.

In the Laundry

You can save a large amount of water by connecting your washing machine to your tank.

Washing machines can use up to 150L of water per load and most households do 5-6 loads of washing per week. A four star front loading washing machine only uses 47L per load.

How big does the water tank need to be?

A good rule of thumb is to purchase a tank that holds a minimum of four weeks supply. For instance, if you use 1,000L of tank water each week in the garden, toilet and laundry combined, you should consider purchasing a 4,000L tank.

Other factors to consider…

  • How big is your roof?
  • How much rainfall do you get in your area?
  • How much space do you have for a tank?
  • What type and size is your garden?
  • How many people live with you?

If your tank is going to be large, consult a builder or engineer as it may require structural support. You may also need a building permit from your local council.