## What is a first flush system?

First flush diverters are a critical component in any Rain Harvesting system. These devices divert and capture the most contaminated, sediment-laden water that washes into your pipes from your roof during the first initial millimetres of rain.

How do you calculate first flush?

First flush calculations As a rule-of-thumb, contamination is halved for each mm of rainfall flushed away. Calculation: meters squared (roof area) X pollution factor= liters to be diverted.

### How long should a first flush diverter be?

Rain Harvesting First Flush Diverters are sold in kit form – just add the desired length of standard 3”, 4” or 12” PVC pipe to create the diverter chamber section.

What is the function of a first flush and filter in rainwater harvesting system?

First-flushing A first flush device is a valve which ensures flushing out of first spell of rain away from the storage tank that carries a relatively larger amount of pollutants from the air and catchment surface.

#### What does a first flush diverter?

A first flush diverter (also known as a roof washer) is a simple contraption that diverts the first flow of water away from a rainwater catchment system. The idea is that diverting the first flush can help ensure cleaner water in your rain tanks or barrels.

How do you size a first flush diverter?

Just remember that you need to size your first flush diversion chamber based on the size of the roof area that’s upstream from your diverter. If two or more pipes (aka lines) feed into a single diverter, you should size your diversion chamber accordingly by considering the total roof area that feeds both pipes.

## How does a first flush diverter work?

A first-flush diverter “washes” the roof, so there is less rubbish on the tank’s bottom. This design works because the bends in the pipe at the top of the diverter keep the first-flush water from flowing back into the tank. The diverter fills up with the first flush of rain from the roof.

How much water does a first flush diverter use?

Most literature cites 5-10 gallons of water per 1000 square feet of roof area should be diverted.