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Benefits of Rainwater Tanks

Friday, April 01, 2016

Have you noticed how, in recent years, our rainfall patterns and our climate are changing? This is all part of a larger global picture, but we all need to plan for changes happening locally. As we continue to experience tighter water restrictions and rising costs, maybe its time to consider installing rainwater tanks. The average home could easily harvest 100,000 L each year from their roof, and this water can be used to offset the water budget for your home. 

Installing a rainwater tank, no matter what size, is a small step that you could take to become self-reliant. Generally, the larger the tank the more water you can collect and use. If you wanted to use rainwater to flush toilets and provide water to the laundry, then you would probably need at least a 9,000 L tank. It is not uncommon to install 30,000 to 50,000 L tanks for this purpose.

What are the benefits of rainwater tanks?

Collecting rainwater has many environmental benefits, as well as benefiting you! Some reasons for harvesting rainwater include: 
  • Making fresh water available to flush toilets or to provide a laundry source.
  • Using rainwater for drinking purposes.
  • Supplementing the watering of garden areas.
  • Reducing our use of mains (scheme) water - a very valuable, limited resource.
  • Saving some money – buying less water from a service provider.
  • Providing a water source which has reduced levels of salts and other substances.

Types of tanks

Rainwater tanks are now made from a variety of materials. Generally, the most popular for urban backyards are either made from steel or from polyethylene. Large tanks (50,000 L plus) are typically steel-liner tanks. These have a steel outer structure with a flexible poly liner inside. These days poly tanks are UV stabilised and come in a range of colours. Both steel and poly tanks normally have a 20 year warranty. If there is space below the house or verandah then a bladder tank is an option. These tend to be proportionally more expensive, but can be ideal if there is little room for a regular tank. Finally, more and more tanks are being buried as new homeowners build larger house on smaller blocks. Below-ground tanks can be buried under decking provide there is access to service the pump or to clean out the tank if required.

Connections to the house

Most people want to use the rainwater - either for drinking or to flush toilets or to wash clothes. Rainwater is most often pumped to the house, although gravity can be used in some cases to direct rainwater to fixtures in the house. Either a submersible pump, a pressure-tank pump or a pressure-switch pump is used to supply rainwater when required. When the tap is turned on, or the toilet flushes, the pump is activated and gently pumps water to fill the cistern, or enter the kitchen sink or washing machine.

What happens when I run out of rainwater?

If you only install a small tank (e.g. less than 20,000 L) then it is likely you will run out of rainwater during the summer period. This, of course, depends on the uses of the rainwater. Providing a full laundry, kitchen and bathroom service rapidly depletes the volume you can collect during rainy times. 

Water Installations installs rainwater tanks that integrate the mains (scheme) water source with the rainwater source. Ross Mars, Managing Director of Water Installations, explains that an automatic top-up device enables mains water to enter the system when the rainwater is depleted. “There are several ways to achieve this, from manually changing valves to fully automated switching devices. It is important to always have water to flush toilets and to provide a source to the laundry” he said.

What you should also consider

Most rainwater tanks come supplied with a basket (leaf) filter, tap and overflow pipe. In addition to these standard fittings, a number of optional extras are available for your rainwater tank system. These include:
First-flush device. This enables the first rains to be directed away from the tank. This water may contain dust and decayed matter, and it is best not to collect this and pollute the tank water.
  • Vermin proofing. This is often necessary for steel and steel-liner tanks to prevent insects, frogs and small rodents from finding their way into the tank.
  • Garden overflow. Either a subsurface piped trench or a simple gravity-fed dripper system is installed to direct overflow more effectively to garden areas or beds.
  • Leaf eater. This is a screen which filters rainwater and allows leaves to be shed from the system.

What are the costs involved?

Rainwater tanks are relatively cheap. However, small tanks are proportionally dearer, so the larger the tank the better is the cost-effectiveness. If you intend to pump rainwater to flush toilets and so on, then a pump and irrigation filter would be required. Installation would be extra, and this depends on the distance to the house fixtures and the degree of difficulty in supplying water to the house. Adding options such as a leaf eater and a first-flush device, overflow to gardens and a filter bag is highly recommended.

You should also check with your local council, as some fees may be applicable for a permit to install a rainwater tank.

Some local government councils also require engineered drawings from the tank manufacturer, and these should be included in the submission to council.

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