Increasing first flush capacity from roof

Hello

My roof area is 150 m2. So this means I would need about 80 liters first flush. My downpipe from the roof is 4 inch diameter and 5.7 meters long and the volume is 45 liters. How can I double my first flush? I don't have space for another pipe next to it.

Where did the 80 L figure come from ?
Do you have lots of dust, trees, bird poo?
Some diverts have spirals  or cyclones so less water is dumped.

John C Daley wrote:Where did the 80 L figure come from ?
Do you have lots of dust, trees, bird poo?
Some diverts have spirals  or cyclones so less water is dumped.

Hi

0.5 liters per sqm. We have alot of dust around here because of tractors. I thought I'd have to clean the top layer at least before it enters the tank. I think I have solved the problem, I'm going to replace the 4 inch downpipe with a 6 inch which should give me 90 liters of storage. I will use that in the garden. The question is, how much filtering do I need to use the remaining water to take showers and wash dishes?

How big is you tank and what rainfall do you get

We don't do these complicated things in Australia, just a leaf eater that's it. The real bad (aluminium etc.) probably does not get eliminated by the first flush device anyway, but I can't say that for sure.

First flush units are used often in Australia, I have installed 100's around Bendigo

But I haven't seen anyone calculataing this. I could take a photo of ours, it has to be emptied every now and then.

John C Daley wrote:How big is you tank and what rainfall do you get

The tank is around 50 tons (concrete tank). Rainfall is around 350 mm per year on average.

50 tons may be the weight of the tank, but not its volume.
The best way to settle and clean water us to have a large tank.
Filters etc are not needed if the tank is big.
350mm is low rainfall, how big is your family?

I would think about having thefirst flush be captured in another tank to be used in an orderly manner, with such low rainfall.

John C Daley wrote:50 tons may be the weight of the tank, but not its volume.
The best way to settle and clean water us to have a large tank.
Filters etc are not needed if the tank is big.
350mm is low rainfall, how big is your family?

I would think about having thefirst flush be captured in another tank to be used in an orderly manner, with such low rainfall.

Sorry I meant 50 metric tonnes which is 50 m3. We have 4 occupants currently.

ok 50,000L thats a good tank size to allow the water to clean itself.
Filters etc into the house would not be needed.

on another post recently I explained how to calculate water flow off the roof and usage by a house hold.
That tank is a good start but you may have to top it up from time to time, can you?
It is certainly big enough to allow the water to clean itself.

From the figures below you will see you will have a usage of 2000L per week if you have flush toilets.
How long are your dry spells?

Tank size needs to be calculated based on the roof area draining to the tank times rainfall amount times weeks of capture.
So you have about 80 sq m of roof [ 780 sq ft ] x 10 weeks x 25mm
= 80 x 250mm
= 80 x .25M
= 20 cubic M which is 20,000 Litres or about 5000 gals.

So if you have 6 weeks of no rain you have about 830 gals a week for watering. [ 3200 L]

In normal times you could capture about 2000L a week.

BUT if you use some if the rainfall each week in the house itself
You would never have enough to keep watering over 6 dry weeks,

With a family of 4 your use could be;
If you can use that same water in the toilets you would use  per person a week 350L........................................1400L
Machine machines between 40 -130L per wash front loader / top loader. times say 1 wash per person = 130 L.....560 L
Garden watering is dependant on many things, but say 1100L per week.........................................................1100 L
Giving a total usage of garden and house af about ....................................................................................  3060 L

So you could think about capturing water off other parts of the roof.

If you have town water, tanks are expensive, if you dont then whilst its still expensive its better than no water.

If you have a well, then there are other large expenses as well.

We have flush toilets that go to a vermifilter. We use around 4000 liters a month at the moment. We can top it off with water from the municipality.

What is needed for the tank to be self filtering?

What do you mean by 'self filtering' ?

John C Daley wrote:What do you mean by 'self filtering' ?

How can you help the tank to clean the itself?

John C Daley wrote:What do you mean by 'self filtering' ?

How can you help the tank to clean the itself?

After water passes through the first flush, then a leaf separator, all the water will enter the tank.

Attach a hose to the inside of the fitting you draw the water from, but on the inside not the outside as is normal and attach a float to it so
the hose with a filter can sit just under the water surface at full tank level.

Any water you draw will come only from near the top, because all the sediment will be settled at the tank bottom and the water generally will be oxygenated.

the volume of the tank will be available to allow settlement and standing time.

Also, a syphon system fitted to the overflow can be set up to suck any sediment off the tank floor whenever the tank overflows.