Rainwater is our principal water source and it will 'collect' and 'carry' anything in its path. These contaminants need to be separated out to improve the water quality before storage or re-use. Capturing rainwater before it is contaminated to any degree is best achieved from an inert catchment such as a clean roof.
A 'First Flush' process uses the initial 2mm to 3mm of rainfall from a rain event to wash down the roof and carry the contaminants into drainage before harvesting commences. This first flush volume has been determined from research to reduce the contaminate load of the rainwater by at least 50%.
The first flush device also continues to trap and separate out sediment for the whole rain event which has the benefit of giving good quality water for storage which may not require further treatment before use, however that occurs.