Rain Harvesting 100mm First Flush Plus
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.
WDDP11 | 100mm
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.
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.
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.
Downpipe First Flush Water Diverters improve water quality and reduce tank maintenance by preventing the first flush of water, which may contain roof contaminants, from entering the tank. They help ensure cleaner water is available for use, which protects rainwater pumps and internal household appliances such as clothes washing machines, toilets, hot water systems, etc.
Features and Benefits
- Prevents sediment, bird droppings, spiders, insects, mosquito eggs and debris from entering the rainwater tank.
- Improves water quality, protects pumps and internal appliances.
- Ideal to use in conjunction with a rain head.
- Easy installation, just add pipe and glue.
- No mechanical parts.
- Low maintenance requirements.
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.
- Determine the length of 100mm pipe required for your first flush diversion chamber. As a rough guide: 1 metre of 100mm pipe holds approximately 8.8 litres of water. Ensure all cut edges are clean and smooth.
- To attach the threated coupling to your diversion chamber pipe, insert a length of male 100mm pipe inside the threaded coupling and glue in place using an appropriate sealant. Glue the other end inside your diversion chamber pipe. Attach the threaded coupling to your diversion chamber pipe applying solvent weld glue to the socket of the coupling and pipe, then push together and hold until the glue sets.
- Select the appropriate flow control washers and fit it into the hose connector with the side marked “TOP” showing. Save the remaining washers for possible future use. Start by using the Control Washer with the smallest gauge hole (lowest number). Try a larger gauge Washer if experiencing blockages. Save the remaining washers for possible future use.
- Insert the plastic filter screen in through the base of the screw cap with O-ring seal and secure by attaching the hose connector and flow control washer.
- Attach the screw cap with O-ring seal (and assembled components) to the threaded coupling.
- Measure your existing downpipe and cut to create space for the T-junction. Your diverter must sit at least 150mm from the ground when fully assembled, so select your installation point and measure and cut accordingly. Ensure all cut edges are clean and smooth.
- Connect the T-junction to the existing downpipe and install with solvent weld glue in the same manner as step 2.
- Insert the ball seat into the T-junction, with the narrow end of the seat facing down.
- Place the ball inside your first flush unit through the upper end of the diversion chamber pipe.
- Apply glue to the T-junction and upper end of the diversion chamber pipe and insert the pipe into the junction and hard up against the ball seat, holding until the glue sets.
- Position your assembled first flush diverter in place and attach to the wall using the supplied brackets, supporting the unit until it is fully secured. The upper bracket must sit directly under the T-junction, where it will hold the weight of the unit.
What comes in my first flush diverter kit?
The exact components included in your first flush diverter kit will depend upon the product you order and are listed on each individual product page.
Where should I install my first flush diverter?
Your first flush diverter can be installed anywhere between your roof catchment area and your rainwater tank to isolate and capture the first “flush” of dirty water at the beginning of a rain event. You may choose to install smaller diverters to divert rainwater from each downpipe or you may choose to install larger diverters to divert rainwater from several downpipes.
How much water should I divert?
In areas with mild pollution (e.g. open fields, no trees, no bird droppings or animal matter, clean environment) you should divert 0.5 litres per square metre of roof (0.0125 gallons per square foot of roof). In areas with higher pollution (e.g. leaves and debris, bird droppings, animal matter/carcasses, pollution) you should divert 2 litres per square metre of roof (0.05 gallons per square foot of roof). These formulas will help you calculate your total diversion volume or, if you’re using more than one first flush diverter, the volume of water you should divert in each device (which will depend upon the size of the roof area that “feeds” each diverter).
How long should my first flush diversion chamber be?
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 100mm pipe = 8.8 litres
1 metre of 150mm pipe = 18.8 litres
1 metre of 225mm pipe = 45 litres
1 metre of 300mm pipe = 72 litres
3 feet of 3″ pipe = 1.5 gallons
3 feet of 4″ pipe = 2 gallons
3 feet of 12″ pipe =19 gallons
Can I run two or more pipes into one first flush diversion chamber?
Yes. Just remember that you need to size your first flush diversion chamber based on the size of the roof area that’s upstream from your diverter. If two or more pipes (aka lines) feed into a single diverter, you should size your diversion chamber accordingly by considering the total roof area that feeds both pipes.
Which flow control washer (valve) should I use?
Your first flush diverter comes with a range of flow control washers (valves). Each washer has a different sized hole. The size of the hole determines the rate at which your first flush diversion chamber will empty. A smaller hole will create a slower flow rate and release less water during a rain event, while a bigger hole will create a higher flow rate and release more water during a rain event. (Blockages excepted, any size washer will eventually fully empty your diversion chamber after each rain event.) Washers with a smaller hole will become blocked sooner than washers with a larger hole. Choosing your flow control washer is therefore a trade-off – lower wasted water during rainfall means more regular maintenance, while moderate wasted water during rainfall means less maintenance is required. However, when choosing your flow control washer, remember that the volume of water flowing from the largest washer, which has a 2mm diameter hole, will still be insignificant when compared to the rainfall flow rate.
Which way should the ball seat be oriented?
Your diverter’s ball seat is like a funnel: /. The narrow end is installed facing down so it can be sealed by the black ball.
How do I plumb the trickle feed outlet on my first flush diverter?
You can use 12mm irrigation tubing to plumb the trickle feed outlet to a location away from the diverter.
How do I clean my first flush diverter?
Slowly unscrew the black hose fitting from the bottom of your first flush diverter. If the diversion chamber is full of water, take care as the water empties. Remove the plastic filter (it may come out when you remove the black hose fitting) and wash under clean water. Check the flow control washer for any blockages and wash with clean water, then replace all these parts.