First Flush Advanced Downpipe Water Diverter | Rain Harvesting by BMCo

First Flush Advanced

First Flush Diverters
Divert more contaminants and take greater control over your water volume with this next generation First Flush Advanced Diverter.
Size 100mm WDDP20
First Flush Plus Tee

Keep more contaminants out

The First Flush Advanced is more effective at diverting contaminated water. Its patented high-flow inlet largely solves the problem of fast-moving dirty water “skipping” over or around the diverter entrance on traditional T-junction first flush diverters.

Arv Web 1

Control quality and volume

With its electronic advanced release valve, the First Flush Advanced gives you greater control over how frequently you release your diverted water. Increase your release frequency to maximise water quality or release the dirty water less frequently to maximise stored water volumes.

Arv Web 2

Maintain with ease

Maintaining your First Flush Advanced couldn’t be easier. The transparent exit funnel allows for easy visual inspection, while the funnel’s tapered shape draws sediment into the exit flow to reduce build-up and blockages. You can also use the rapid-exit valve to fully empty the diverter as required.

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

Maelstrom Filter
Maelstrom Filter
Leaf Eater Advanced
Leaf Eater Advanced
90mm or 100mm
Easy Clean Tank Overflow Kit High
Easy Clean Tank Overflow Kit High
90mm (with Easy-Clean)

Your selection

Add Rain Harvesting or Plumbing products to your list.