First-Flush Diverters: Keeping the Dirty Water Out of Your Tank

When rain starts, the first few millimetres wash dust, leaf litter, bird and possum droppings off the roof and gutters. A first-flush diverter catches that dirty water in a pipe or chamber so it never reaches the tank.

1. How it works

A vertical pipe fills first. Once it's full, a ball or float seals it and the cleaner water flows on to the tank. A small drip outlet slowly empties the pipe so it's ready for the next rain.

2. How big

A common rule of thumb is to divert somewhere between 0.5 and 2 litres for every square metre of roof feeding it. Dusty areas, overhanging trees and long dry spells call for the top end. Follow the diverter maker's sizing chart.

3. Keep it working

• Clean the screen and drip outlet every few months. A blocked outlet stops it resetting.
• Check the ball or float moves freely.
• Keep the gutters clean and trees trimmed back.

4. Drinking water

A diverter helps, but it doesn't make water safe to drink by itself. Ask your local council or state health department about treating rainwater for drinking.

5. Quick summary

• The first flush carries most of the roof dirt.
• Size it for your roof area and conditions.
• Clean the outlet and screen regularly.

General information only. Check the maker's instructions, and ask your council about approvals.

← Back to all guides