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First Flush Diverters: The Optimal Solution

A first flush device is designed as a low maintenance diverter to prevent dirty water entering the tank from the roof.

A first flush diverter is designed to operate automatically. It does this by diverting a predetermined amount of water from the roof. After the predetermined amount of water has been diverted, the rainwater then flows directly to the rainwater tank. First flush devices are designed to be low maintenance. They automatically empty through a small outlet. However, they are not maintenance free. They should be checked regularly to ensure that any build-up of dirt does not adversely impact on the performance of the diverter or prevent the captured water from dispersing. 

The operation of a simple first flush device can be seen in this animation.

First Flush Diverters: Where Do They Go?

In theory a first flush device should be just before the rainwater tank so it is diverting all of the dirty first water. If the location of the tank or nature of the installation does not allow for a single first flush device, then multiple first flush diverters may be required. A more economical solution may be either a centralised first flush device (either on a wall, under a floor area or underground) or a single in-line whole-of-roof filter.

The optimal first flush solution is usually determined by the local environment, the nature of the water storage and the site where the system is being installed.

Commercial First Flush Diverters

First flush diverters are now available in commercial sizes of 150mm and 225mm diameter pipes. In addition, with the use of standard pvc pipe adaptors, the diameter of the first flush pipe can be further increased to maximise the amount of storage for the available space. In particularly large rainwater harvesting systems, a separate rainwater tank may be used as a first flush diverter.

For more information, visit the first flush device information page or contact the team at Waterplex on 1300 72 66 70.

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