Rainwater tanks, are becoming a more common feature in urban communities, with around 17% of all households installing a tank on their property. More households need to purchase a rainwater tank if the community is to make a real difference to conserve rapidly depleting water supplies.
Why use rainwater?
• Using rainwater can reduce your water bills.
• Collecting rainwater allows you to be prepared for times of low rainfall, so you can still maintain your garden, especially if there are water restrictions in your area.
• It reduces the load on stormwater systems because roof runoff is not flushed into the drains.
• Using rainwater reduces the need to build more water storage dams, which may have to be situated in environmentally sensitive areas.
Benefits of installing a rainwater tank.
• Saves water which can be used in the garden or in the home.
• Requires a relatively simple system which is easy to use.
• During the wet season, when the garden doesn't need any extra watering, rainwater can be connected to the house and used for toilet flushing as well as in the laundry.
• Rainwater is also suitable for use in pools and for washing cars
• In some rural areas, it is possible to use rainwater for all domestic uses, and not draw upon the mains supply.
Issues associated with rainwater use.
There are some important factors that affect the quality of rainwater, which may also become health issues:
• Contamination from pollutants found in roof and pipe materials.
• Contamination from bird droppings, local pollution, and organic material collected on the roof.
• Breeding of mosquitos in the water supply.
The quality of water you need to maintain will depend on its use. However, water from rooftops that contain harmful chemicals should not be used for any purpose. Obviously, drinking water will have to meet the standards set by health authorities.
These quality issues can be overcome if you use approved products and techniques. Tanks and other equipment must meet the required standards, and state health authorities will approve most reputable manufacturers and installers. Your local water authority should be able to recommend high quality products and approve your system.
What size tank will I need?
As a general rule you should install the largest tank that you have room for or can afford. This will allow you to use rain water for as long as possible through droughts and prolonged dry periods.
Tank Size - Rule of thumb.
A good rule of thumb is it should hold a minimum of 12 weeks supply. For instance if you use 1,000L of tank water each week in the garden, toilet and laundry combined, purchase a 4,000L tank. This will mean that the tank will only be empty through extended dry periods.
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?
It is a good idea to install a larger tank as you will be less likely to run out of water during prolonged dry periods. 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.
How much rainfall will I get?
The pattern of rainfall is important, if you have very regular rainfall all year round, you can use a smaller tank. Average rainfall across Victoria varies from 200mm to well over 1000mm per year or over 5000mm per year in some places in NSW. For information on rainfall in your local area, contact the Bureau of Meteorology at www.bom.gov.au and check out the rainfall maps.
How much rainfall will I collect?
You can find out the amount of rainwater you will collect as each square meter (m2) of roof area collects 1L of water for every 1 millimetre (mm) of rainfall received.
This is determined by the area of roof connected to the tank via the storm water down pipe.
As an example:
An average house has a roof area of approximately 160 m2.
Assume that 50% of this roof area can be easily connected to a rainwater tank i.e. 80 m2
Each m2 of roof area collects 1L of water for every 1mm of rainfall received.
If you have 10 mms of rain the water collected by the tank is 800L (80 m2 x 10 mm = 800 L).