First Flush Plus Diverter | Rain Harvesting by Blue Mountain Co

First Flush Plus

First Flush Diverters
Protect your rainwater quality by diverting the most contaminated water that washes off your roof with the first few millimetres of rainfall using the Rain Harvesting First Flush Plus.
Size 100mm WDDP11
First Flush Plus Tee Resized

Install with ease

Supplied in kit form, the first flush diverter can be installed on your downpipes with a simple T junction. Simply add and install the length of pipe required to meet your diversion needs. This will be based on the volume of dirty, contaminated water you wish to divert.

First Flush On Blue Tank Next To Vege Patch

Improve your water quality

Help prevent hazardous organic and inorganic particles from contaminating your rainwater by diverting and discarding the most particle-laden water from your roof. This first flush diverter captures the first flush of rainfall so you get better quality water in your tanks.

End Cap With Flow Controllers FF

Use your diverted water

The water you divert is automatically released through the slow release valve. You can empty this water into a standard drip irrigation system for use around your garden or you can direct it into stormwater drainage. The choice is yours.

Calculate your diversion needs

Generally speaking, the more water you divert, the better the quality of the rainwater that ends up in your tank. However, diverting more rainwater than necessary can lead to volume shortages, so it’s important to calculate your diversion needs, and divert water accordingly.

The following formulas offer general guidelines for calculating how much water you should divert:

  • Areas with low pollution (open fields, no trees, no bird droppings or animal matter, clean environment) = divert 0.5 litres of water per square metre of roof
  • Areas with higher pollution (leaves and debris, bird droppings, animal matter/carcasses, pollution) = divert at 2 litres of water per square metre of roof.

This calculation will allow you to determine what length and size pipe or pipes you need for your diversion chambers.

The length of pipe required to form your first flush diversion chamber will depend upon how much water you need to isolate and capture.
The following measurements are given as a guide only.

1 metre of 90mm pipe = 5.7 litres
1 metre of 150mm pipe = 18.8 litres
1 metre of 300mm pipe = 72 litres
3 feet of 4″ pipe = 2 gallons
1 metre of 100mm pipe = 8.8 litres
1 metre of 225mm pipe = 45 litres
3 feet of 3″ pipe = 1.5 gallons
3 feet of 12″ pipe = 19 gallons

First Flush diverters help you plan for volume by allowing you to choose your catchment volume with custom catchment size and/ or an advanced release valve.

First Flush Diverters help divert the first flush, through their design. They are installed using a T junction or high flow inlet to which the diversion chamber is fitted. As the chamber fills with the initial dirty water from your roof, a ball rises until it seals the inlet, allowing the rest of your rainwater, which is much cleaner, to flow directly to your tank.

Learn more about the 4 pillars of designing a Rain Harvesting system. 

The Rain Harvesting steps addressed:

Limit sources of contamination     Plan for volume

Filter leaves and debris                    Divert the first flush

Secure the system                             Manage standing water

Consider a safety net                        Monitor and maintain

Products you may be interested in

First Flush Advanced
First Flush Advanced
Maelstrom Filter
Maelstrom Filter
Leaf Beater
Leaf Beater
90mm or 100mm

Your selection

Add Rain Harvesting or Plumbing products to your list.