Pour éviter de récolter les saletés du toit, un système de chasse permet de jeter les premières précipitations "sales", pour ensuite conserver l'eau "propre".
What is a First Flush System?
In a typical rainwater harvesting system rainwater is collected that lands on a roof and is then chanelled down through guttering and pipework to a storage tank. During dry periods of weather the roof gets covered in a fine coating of dust together with leaves, bird droppings, and other debris. When it starts to rain these objects are washed straight off the roof and down the guttering. After a certain quantity of rain has fallen the loose dirt and debris is virtually all washed away and the water coming down the pipe can be assumed to be clean.
A First Flush System dumps the water that comes down the pipe first since it may be contaminated, and only when the rainwater coming down the pipe is clean does it get directed into the storage tank.
Example of First Flush Systems
First flush systems are available commercially, but DIY systems can be put together using easily and cheaply available parts. The two commonest systems use either a floating ball or a tipping gutter to divert and/or store the first flush away from the storage tank.