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Rain Harvesting Pty Downspout First Flush Diverter

The RainHarvestingŪ First Flush Downspout Diverter. A simple and effective first flush water diverter that requires minimal maintenance.
First Flush

Product Code: WDDS9X

Currently in stock

Rain Harvesting Pty 3" First Flush - $29.95
Rain Harvesting Pty 4" First Flush - $34.95

Downspout first flush diverter
Clear tube shown is for illustration only
When it rains, water slowly builds up in the roof gutter system before it exits through the downpipe. The first flush of water from the roof can contain amounts of bacteria from decomposed insects, lizards, bird and animal droppings and concentrated tannic acid. It may also contain sediments, water borne heavy metals and chemical residues, all of which are undesirable elements to have in a water storage system.

Instead of flowing to the water tank, these pollutants are diverted with the initial flow of water into the chamber of the water diverter. The water diverters from Rain Harvesting utilize a dependable ball and seat system - a simple automatic system that does not rely on mechanical parts or manual intervention.

As the water level in the diverter chamber rises the ball floats, and once the chamber is full, the ball rests on a seat inside the diverter chamber preventing any further water entering the diverter. The subsequent flow of water is then automatically directed along the pipe system to the tank.

For a Water Diverter to work effectively, the contaminated water in the chamber must be sealed off. This prevents the contaminated water from passing to the storage tank and ensures the water does not "siphon" off the contaminated water in the chamber. The simplest and surest way to do this is with a floating ball and seat.

A slow release valve ensures the chamber empties itself after rain and resets automatically. The diverted water need not be wasted water because the drain pipe from the diverter chamber can be fitted to a standard drip irrigation system.

rainharvesting first flush diverterSimple and effective first flush devices, these are installed at the downpipe and used when there are a small number of downpipes supplying water to the tank.

It is preferable to fit the longest length chamber possible to ensure better quality water. Install the chamber below the gutter filter (or rain head), to within 6" above the ground to allow easy access to the end cap.

Downpipe Diverters should be installed at each downpipe that supplies water to the tank. For systems with multiple downpipes or high volumes of water, a Post/Wall Mounted Diverter or In-Ground Diverter may be more effective.
Rainharvesting First Flush DiverterThe diverters are supplied in kit form and come with everything needed to complete installation - just add the length of PVC pipe required to form the diverter chamber.

Water Diverters work best when a gutter downspout filter (sometimes called a rain head) is installed upstream of the diverter. Fitted at the downpipe either directly on the underside of the roof gutter or to a wall, the Leaf Eater or Leaf Beater rain heads, also from Rain Harvesting, are self cleaning devices that deflect leaves and debris away from the flow of rainwater. Rain heads ensure the diverter chamber and Slow Release Control Valve do not block up as easily. They not only help Water Diverters operate more efficiently in preventing fine sediments and pollutants from entering the rainwater tank, they also ensure Water Diverters drain and reset automatically after rainfall, significantly reducing system maintenance.

An optional stainless steel primary screen is available. The stainless steel screen provides extra confidence with additional filtration of fine sediments and pollutants to ensure the slow release control valve does not block.

Diversion Recommendations for the Roof

Minimal Pollution: divert 0.0125 gallons per square foot of roof area
Open field, no trees, no bird droppings, clean environment

Substantial Pollution: divert 0.05 gallons per square foot of roof area
Leaves and debris, bird droppings, various animal matter, e.g. dead insects, lizards, etc.


Example for a minimal polluted roof of 1,000 square feet:
1000 square feet X 0.0125 = 12.5 gallons to be diverted

Example for a heavily polluted roof of 1000 square feet:
1000 square feet X 0.05 = 50 gallons to be diverted

PVC Pipe Specifications

3" Downspout diverters: Use 3" Schedule 40 PVC
(not sewer and drain pipe)
Storage capacity: Each 3 foot section of 3" PVC holds approximately 1.1 gallons of water (0.3840341 gal/ft)

4" Downspout diverters: Use 4" Schedule 40 PVC
(not sewer and drain pipe)
Storage capacity: Each 3 foot length of 4" PVC holds approximately 2 gallons of water. (0.661312 gal/ft)

12" First flush diverters: Use 12" Schedule 40 PVC
Storage capacity: Each foot of 12" PVC holds approximately 6 gallons of water. (5.81463286 gal/ft)


Downspout first flush diverter assembly
rainharvesting first flush filter legend



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