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Benefits of First Flush Devices



Stan Abbott of Massey University in Wellington, New Zealand, was commissioned by the New Zealand Government’s Ministry of Health to investigate measures that can be taken to improve the water quality from rainwater harvesting systems. Abbott established New Zealand’s most sophisticated Roof Water Research Centre (RWRC) on campus and thousands of samples were taken from a series of different systems.

Abbott concludes from the preliminary results that the quality of the water improves dramatically with the use of first flush water diverters. These findings reinforce the importance on diverters and screened downpipe rain heads in overall system design.

Download a summary report on the research.




First Flush Water Diverters are a critical component of rainwater harvesting systems. By preventing the first, most contaminated water from the roof they:

1. Improve rainwater quality and safety

2. Help extend the life of pumps (used to distribute rainwater for use) and internal appliances (such as hot water systems, washing machines, dishwashers, etc)

3. Reduce tank maintenance

The First Flush Water Diverters from Rain Harvesting, are simple to install, operate automatically to help prevent pollution of tank water, and are available in a number of different sizes to suit different requirements.

They operate best when used in conjunction with the Leaf Eater® range of rain heads. When fitted upstream of a First Flush device, the rain heads will prevent leaves, debris and other organic matter away from the flow of water. The First Flush Diverter then ensures that heavy sediments and other finer pollutants are captured in the diverter chamber.





Leading pump manufacturers, such as Davey, recommend the use of First Flush Water Diverters to help extend the life of pumps.rain_bank

Typically pumps utilise a mechanical seal to ensure water does not penetrate into the pump’s electric motor. First Flush Devices help prevent sediments and other debris from:

1. Wearing down the seal (which can result in pumps leaking),
2. Getting caught in the pump impeller,
3. Jamming up other pump components.

The Installation and Operating Instructions (as at 29 March 2006) of the Davey Rainbank, an innovative product that allows the priority sourcing of rainwater, only using mains water as backup, make the following recommendation:

“Your rainwater tank may be required to be installed with a first flush diverter. Installing a first flush device is essential to reduce the introduction to the rainwater tank of sediment and other materials which can pollute the water. Even where it is not a requirement of your local water authority, Davey recommend the use of a suitable first flush diverter and/or rainwater inlet strainers.”