That's where a first flush device comes in. A first flush device, also known as a water diverter or a first flush diverter, is an add-on to your water tank's rainwater harvesting system. This add-on lets you screen out leaves, bird droppings, dirt, and other contaminants that come from your roof when the rain first begins so that the water that's collected in your water tank will be clean and clear as nature intended.
The way that your standard first flush water diverter works is fairly simple. As water enters the pipe that leads to your water tank, it falls down into the first flush device instead. The device is essentially a chamber that's long enough to catch all of the first flush rainwater which is filled with the dirt, bacteria, and other contaminants from your roof. Inside the chamber is a small ball which will float on the water but that is too large to fit through the opening at the top of the chamber. As the water fills the chamber the ball will continue to rise, essentially closing off the mouth of the chamber when it can't fit through. From this point, all of the clean rainwater that flows through will go directly into your rainwater tank instead of the first flush chamber.
Once the rain has stopped, emptying the chamber of your first flush device is automatic. A release valve on the bottom of the chamber will slowly let water escape (and since the rain has stopped, it won't keep filling up again.) To further improve the environmental impact of your water tank, you can even hook the release valve up to your irrigation system so not even the first flush water goes to waste. Most first flush filters require very little maintenance. Occasionally leaves may block up the drainage of the first flush so you may need to clean it out occasionally. This isn't normally a big problem because the chamber empties very slowly so even if it is blocked it should still be able to drip. The biggest concern is that a blocked first-flush system may become a breeding ground for mosquitoes. If you get a lot of leaves and rubbish then it may need to be cleaned a couple of times a year and will provide you with nice clean water for many years.
