Treatment MeasuresRain Water Tanks : Maintenance & Costs
More Information
Water Quality In Rainwater Tanks
Water quality is a potential problem with all roof water systems, especially in urban and industrial areas. However, this is unlikely to be an issue if they are only used for outdoor use, laundry and toilet flushing. If you choose to use your rainwater supply within the household (ie laundry, toilet flushing), appropriate 'back flow' prevention devices should be in place to protect the water quality of your household mains water.
Water quality problems include:
- Atmospheric pollution, particularly in industrial areas.
- Bird and possum droppings which can pollute the water with bacteria and gastro-intestinal parasites.
- Insects, lizards and other small animals which can get into a tank and may die there.
- Roofing material and paints. For example - lead based paints in particular should not be used on roofs where water is collected (this should not be a problem for roofs painted after 1970).
- Detergents and other chemicals from roofs painted with acrylic paints can dissolve in the run off.
Based on the above information and Melbourne Water's obligation to protect human health, our current position is that use of rainwater tanks for drinking water is not recommended.
Maintenance
Maintenance requirements are;
- Annual flush out of tank to remove built up sludge and debris from the base of the tank.
- Visual inspections of fittings and external surfaces. Most rainwater tanks are installed with ~25 year warranty, therefore this time period is a good estimate of the lifespan of the tank.
Costs
Purchase and installation costs vary considerably with size and supplier. A couple of examples from Australian suppliers are;
- Yarra Valley Water (June 2002)
600L tank (25 Year Warranty, without pump) Fully installed $794 - Other Suppliers start at around $400 dollars with many variations and sizes.
Rainwater collected in this way is not recommended for public consumption without adequate filtering of water in accordance with state health policies.
The cost savings of collecting rainwaters are the use for watering gardens and lawns, washing of cars and the topping up of chemically treated swimming pools.
Costing Example
| Required Information | Example for Melbourne Victoria |
|---|---|
| Annual Rainfall (R) (metres) Area of Roof (AR) (square metres) Capture Efficiency (assumed as 0.6) Initial Cost of Tank (C) Tank Lifetime (TL) years |
R: 700mm (0.7m) AR: 150m² C: $794 TP: 25 years |
Steps
|
105 x 0.6 = 63 kL 63 x 25 = 1575 kL 674 / 1575 = 0.427 dollars per kL |
Cost Comparison
In comparison the cost of domestic (mains) water supply for Melbourne is around $0.723 per kilolitre (June 2002, Yarra Valley Water - Domestic). This equates to a cost saving to the consumer of $0.296 per kilolitre used over the lifetime of the tank. With the tank used at its maximum, the cost over 25 years for using a rainwater tank instead of main water would result in a saving of $466.20.
Further information
If you would like further information on any other aspect of Melbourne Water's role in managing our water resources, please contact us on 131 722 or visit Melbourne Water's website at: www.melbournewater.com.au, or contact your local retail water company (Yarra Valley Water -131 695; City West Water - 131 691; South East Water - 131 694).