First Flush Devices

So, what is a first flush device?

A first flush device is an important part of a good rainwater collection system. It comes in a variety of guises but is essentially a vessel designed to trap contaminants that wash from the roof when it first starts to rain. In effect a primary filter for your rainwater.

The first flush device is located between the gutter and the tank inlet. As the dirty water runs off the roof it fills the vessel. When the vessel is full, cleaner water then flows to the tank. In the base of the first flush is a small weep hole which allows the dirty water to drain, emptying the vessel for the next rain event.
The small weep hole is protected by a fine sieve to prevent the weep hole from clogging with particles.
Periodic maintenance is required to remove and clean the sieve and weep hole.
Benefits of a first flush device:
• Improved stored rainwater quality
• Removal of suspended organic and inorganic fine particles
• Slowing down algae growth and tannin leaching
• Reduced sediment build-up in the tank
• Reduced sediment load on pumps and other downstream equipment and household appliances

If you do not currently have a first flush device on your rainwater collection system, one can be retro-fitted.