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Installing a Rainwater Tank - Part 1 Rainwater Systems

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Starting out: how and where can rainwater be used, selecting the right rainwater system.
For: Plumbers, apprentices, householders

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John Caley

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John Caley B.E. (mechanical) M.E.S. (environmental) MIEAust CPEng

John Caley is the Principal of Ecological Design, a consultancy providing sustainable design services to building designers, developers and individuals. He trained as an engineer but has also worked in bush regeneration, landscaping and installing rainwater harvesting systems.

John has designed rainwater and greywater systems for many developments from single houses to subdivisions.

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One of the great challenges we face is ensuring a reliable supply of water for our growing population. In this series of four short videos we'll explain how you can collect and use rainwater for household use.

We can halve our household water use with simple water smart features like dual low flush toilets, efficient showerheads, appliances and drought tolerant gardens. Rainwater tanks can further reduce mains water demand by using water that would otherwise go down the storm water drain.

Rainwater systems must be installed by a licensed plumber in accordance with  regulations and Australian Standards. For new homes, the rainwater system may be a condition of planning and building approval so check compliance with approved plans. Rainwater systems may be eligible for cash rebates, so check rebate requirements with your local water authority.

What is a rainwater system

There are four components to a rainwater system:
collection ‐ by roofs, gutters and downpipes,
storage ‐ which comes in many shapes, size and types
supply ‐ using pumps, filters and mains back‐up systems, and
use by different fixtures and appliances in the home and garden.

Let's first look at what rainwater can be used for; then we'll look at what you need to know to collect, store and supply rainwater for these uses.

Using rainwater

Thousands of Australians rely on rainwater tanks for all their household needs but health authorities recommend mains supply for drinking water when it's available. If you want to supply drinking water from your rainwater system you need expert advice on its design and installation. In areas with mains water, our focus is on the most effective ways to reduce demand on the mains water supply.

Let's start with the simplest and work up to more challenging applications. One of the simplest uses of a rainwater system is watering the garden. No real issues with water quality. You may not even need a pump. If pressure is required, a suitable pump can be added. Gardens need water most when it rains least, so while tanks can be useful they generally won't provide enough water to get through a dry summer. The best approach to helping the garden survive dry times is to use mulch and drought tolerant plants and grass.

Toilet flushing is a great use for rainwater ? you only need a simple pump and there are few issues with water pressure or quality. Rainwater can be connected to the cold inlet of washing machines. The rainwater must be free of sediment and discolouration. Washing machines need good, consistent water pressure while cutting in and out many times each wash, so your pumping system will have to be up to the task.

You can also supply rainwater to a storage hot water system, though Health authorities recommend using mains water if available. A storage water heater must be set to 60 degrees Celsius to kill potentially harmful bugs, or sterilised by other means. If the cold water comes from the mains, the hot water needs to be at a very steady, constant pressure or it can become impossible to maintain an even temperature in mixer taps or the shower. So make sure you have a suitable pump and control system.

Choosing a system

The rule of thumb is to connect your rainwater system to as many uses as feasible. This minimises mains water demand and the more rainwater you use, the more space you free up in the tank for collection. A typical approach is to use rainwater for garden, toilet flushing and cold water tap for the washing machine, but this will vary from house to house.

You need to match the indoor uses with the amount of rainwater most easily collected.
If you've got a small roof and small tank ? maybe just supply the toilet cisterns.
If you've got a large roof and space for a decent sized tank ? make more use of it.
The appropriate quality of the pump and any filtration equipment depend on use. For example, irrigation or toilet flushing requires just a simple pump with minimal filtration. However, rainwater supply to hot water and other household fixtures requires careful selection of pump, control and filtration equipment. The other videos show how to collect, store and supply rainwater for your choice of uses around the home.

You'll find more information on the Trade Secrets website, including how to get a copy of the Rainwater Tank Design and Installation Handbook. It provides detailed information about all aspects of selecting and installing a rainwater tank.



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