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Rainwater Harvesting Pump Guide

Rainwater Harvesting Pump Guide

4th Jun 2019

For those who only want to water a small garden then fittings to the gutter, a water tank, a hose connector at the bottom of the tank, overflow to your stormwater pipe and a hose is about all you need as long as your garden isint higher than the tanks water level.

On the other end of the scale, there are those who want to water their larger gardens and lawns, wash their cars as well as use the tank water to flush the toilets, wash the clothes in the washing machine and top up the pool or water feature.

The ideal system set up uses a automatic pump and switch system (ie. :-Davey Rainbank, Onga Waterswich, Grundfos Rainswitch, Bianco Rainsaver) which uses tank water, until the water gets below a certain level and then automatically switches the system over to mains water. Having a automatic pumps system like this can save you alot of money by having your tank and pump connected to your toilets and your washing machine, both of which use a lot of water in every household.

In order to estimate pump size we need to understand the flow rates required for house use. The flow rate guide below provides an indication of the flow rate that the pump may need to supply.

Toilet 5 LPM , Washing Machine <12 LPM, Hot Water (shower) <9 LPM, Garden Hose 15 LPM, Sprinkler 15 LPM

As a guide you should assume two appliances could be operating at the one time. An industry standard for the pressure provided by the pump should be greater than 300 KPa.

A pumping system can be installed on a rainwater tank to increase the water pressure to be used for garden watering and inside the house for the toilet, washing machine, or whole of house. Some water appliances will not work unless there is pressure produced by the pump. The pump can be installed outside (external pump) or inside (in-tank pump) the rainwater tank.

Pump Selection - The pump is a key component of a rainwater harvesting system and an investment in quality and reliability from a reputable supplier and brand is recommended. Choose the smallest pump size (measured in Power Absorbed) for the required household flow rate. This will minimise electricity usage.

Use short suction lines when installing - The use of short suction lines will prevent problems with air entrapment. This can cause the pump to loose prime and effect operation of the pump.

Minimise the use of elbows in suction pipework - Position the pump to use the least elbows possible in the suction line. It is best to have no elbows but where necessary have as few as possible. Try to prevent having an elbow directly onto the inlet of the pump. Elbows in the suction line cause performance and noise issues with the pump.

To maximise the efficiency of rainwater harvesting, rainwater should be connected to all outside garden taps and inside the house (toilets, washing machine and/or whole of house). A connection to the mains supply can provide mains water bypass in times of dry weather (when there is no rainwater in the tank)

The rainwater harvesting system uses local rainwater first and switches to a mains water supply when rainwater is not available. This is an optimum outcome because it maximises the yield from the rain harvesting system without having to provide 100% water security. This solution also saves water utilities and government billions of dollars in capital investment and operating costs by reducing water demand and impacts on waterways across the community.

A correctly designed rainwater harvesting system fulfils its requirements without requiring daily supervision or extensive maintenance.

KEY POINTS FOR UNDERSTANDING RAIN HARVESTING

  • Rainwater harvesting systems are inexpensive, easy to maintain, provide a reliable source of water and have greater benefits than costs for the majority of households.
  • Rainwater harvesting saves water utilities and government billions of dollars in capital investment and operating costs by reducing demand for mains water and impacts on waterways across the community.
  • Rainwater harvesting reduces stormwater management costs and reduces the environmental impact of water management in our cities and urban development
  • Over 3 million Australians drink rainwater every day, drinking quality rain water is easily achieved
  • Rainwater harvesting combined with mains water service provides water supply more efficiently than either system alone.

If still in doubt contact us, and we can recommend the most suitable pump for your application.