First Flush Device

ELEMENT:

First Flush Device

AIM:

First Flush devices, also called Water Diverters, are used to ensure only high quality water enters the rainwater tanks.

In between rainfall events dust, car exhaust, leaves and animal droppings accumulate on the roof. During the next rainfall the contaminants are washed into the rainwater tanks. First Flush devices store the first millimetres or so of rainfall, and divert this contaminated water away from the rainwater tanks. The rest of the clean rainwater collected by the roof is directed into the rainwater tank. As a rule of thumb, 100L of first flush is required for each 100m squared of roof area.

The Healthy Home uses four First Flush devices. Each of these has it's own small 25L tank to catch the initial polluted water as well as a fine mesh screen to filter out leaves and other organic debris.

After a rainfall event, the first flush tank empties by discharging through a small drainage hole - this way the first flush device is automatically reset for the next rainfall event.

First flush devices operate by filling of a small storage tank which causes a "captured" floating ball to rise to the top of the tank, thereby diverting all subsequent roof runoff into the rainwater tank.

Click on the diagram on the right to see an animation of a First Flush device.

Click here for Technical Detail.