What is a First Flush Diverter?

First Flush Diverter - What does it do?

The role of the First Flush Diverter is to capture and divert the first few litres of rainwater that washes off from your roof and gutters, and prevents it from entering your water tank. Those first few litres of water are often contaminated, by dust (especially if you live in a windy area), airborne pollutants (if you live near an airport or factories), animal fecal matter (mostly from bird droppings) and leaf debris. Click here to see Recommended First Flush Diverters.

First Flush Diverter components

How does a First Flush Diverter work?

The water container of a First Flush Rainwater Diverter is a vertical PVC pipe with a 80mm or 110mm diameter. Inside this pipe is a ball system - a flotation ball that floats on top of the water. When the water level rises through the vertical pipe and reaches the top, the ball floats at the surface of the water and closes the pipe hermetically, directing the water overflow into your rainwater tank. At the bottom of the First Flush Diverter, the end cap is fitted with a ball valve (or similar) to empty the contaminated water after the rain.

What are the benefits of a First Flush Diverter?

By filling up your tank with cleaner water, the First Flush Diverter will help you:

  • limit the growth of algae, bloodworms, harmful bacteria and protozoa
  • limit the build-up of sludge, contaminants and sediments
  • extend the life of the water pump and filter cartridges connected to your tank

Where do you install a First Flush Diverter?

A First Flush Diverter should be installed just before your rainwater tank, after a Leaf Catcher.  The Leaf Catcher first diverts big debris and leaves, and the First Flush removes smaller debris, animal droppings, pollutants and dust, before they can enter the rainwater tank.

First Flush DiverterFirst Flush Diverter installed below gutter

How big should a First Flush Diverter be?

The bigger the roof, the bigger the First Flush Diverter needs to be. To remove most dirt off a roof area of 50m², a First Flush Diverter should ideally be able to collect about 25L of water. This represents a length of 2.5m for a 110mm First Flush Diverter, or 5m for an 80mm First Flush Diverter.

Recommended First Flush Diverters

First Flush Diverter, 80mm
80mm First Flush Diverter
First Flush Diverter 110mm
110mm First Flush Diverter

Is a First Flush Diverter recommended when harvesting rainwater?

At EcoDepot we always recommend using a First Flush Diverter. It extends the life of your pump and filters, and limits the growth of unhealthy bacteria in your rainwater tank, such as E. coli and Giardia.


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