Rainwater Harvesting Experiences (2022 Edition)

[BristolBuild2020]

Looking for updated RWH thoughts... since this thread:

 

 

I'm currently in the process of specifying my RWH tank, but a number of issues are coming up and I'm really wondering if its worth it, however with this recent drought I really want to store big numbers as even with a 7500L tank at ~200 litres a day for toilets/washing machine thats only 35ish days. I may also need to store large amounts due to soakaway issues (low infiltration  rates...)

 

I also want to irrigate the green roofs with the stored water when its really dry, otherwise pretty pointless using mains water to irrigate the roof!

 

I've collected the data for my location of rainfall for the last 60 years, so I know the best/worst conditions and its not ideal.

 

The issues I have come across:

 

1. Staining

70% is green roof thus discolouration due to solubles due to the substrate is likely.

So I could collect from just the 60-70sqm that isn't green, but barely fill 7500L most years and never fill 15000L.

I was thinking that the majority of the staining is flow through the substrate, thus if I had a way of diverting low flows (<0.1l/sec) to the soakaway then I'd only be collecting runoff and maybe minimise the discolouration?

I can't imagine that even from a non-green roof that its perfectly clear as the leaves/etc that get stuck in the gutters etc also cause a little discolouration?

 

2. Pollen/Surface pollutants

Apparently the tanks should overflow 'regularly' a few times a year, however again using the data, very rarely do they overflow (removing the top surface) unless I pick a pointlessly small tank. So either I need to find something that can skim off the top of the tank irrespective of level or pre-filter the water to remove the top surface again. I have an idea in my head so I might need to sketch it up to see if it works but wondering if anyone else has come across this before?

 

 

Thinking about a large sand filter somewhere on the site to pre-filter the water, but may struggle in downpours...

 

All rather tricky...!

[mike2016]

The Inlet for taking water out of a tank is normally a float, with the intake part a foot or two deeper if I recall to ensure the water is drawn from deeper in the tank to avoid any surface contaminants or turbulence. Check out this site for some resources: https://www.harvesth2o.com/index.shtml

Never thought about collecting off a green roof, my pitch will be difficult one so plan on tile.....

[CADjockey]

Just installed a 7500L tank for toilet flushing, washing machine and watering the garden. Calculations tell me that our usage could be ~71kL and the capture could be ~62kL. Currently not on a water meter, but should significantly reduce our fresh water requirement, and thgeoretically provide 38 days of drought resistance.
 

 

[SteamyTea]

@CADjockey

What are you doing to clean the water before use?

 

[CADjockey]

On 03/09/2022 at 09:29, SteamyTea said:

@CADjockey

What are you doing to clean the water before use?

 

It's filtered before it goes into the tank, and I think it's filtered before it's pumped to the header tank. Therafter it's only used in the, garden, toilets and the washing machine.
The system control provides for recycling to prevent stagnation in the header tank, but it's not being used where mains quality water is required (taps & showers).
 

[SteamyTea]

@CADjockey

Thanks.

I assumed it was something fairly basic.

Do you mean recycling or recirculating to/from the header tank?

[CADjockey]

29 minutes ago, SteamyTea said:

@CADjockey

Thanks.

I assumed it was something fairly basic.

Do you mean recycling or recirculating to/from the header tank?

 

This seems like the simplest bit we are installing what with the GSHP & MVHR !

They call it recycling but yes I think it means recirculating the header tank.
https://www.rainwaterharvesting.co.uk/product/rain-director/

Edited September 4, 2022 by CADjockey
Updates

[BristolBuild2020]

Some updates, due to the poor infiltration rates we are now putting rainwater down a combined sewer at 0.1l/s.

 

However in theory you shouldn't use Driveway run off for RWH...

 

Thus I need at minimum now two tanks, one at-least 10m3. So call that two 7500L (as cheaper than an actual 15m3 tank) to leave me with 5000L that I can use to irrigate the green roof in the summer plus one more for actual use for RWH.

 

Talking with some suppliers, they are quoting BS8515 resulting in a 3000L tank (just collecting off the non-green 54sqm at the moment).

 

However having got the rainfall data for my location for the last 130 years, even with a 3000L tank there a long periods whereby its effectively empty (I assume empty at 200L remaining) and long periods again when it never overflows, yet apparently BS8515 is what we have to design to to ensure fresh water ever 15 days (not quite sure how you can maintain that if it doesn't rain...)

 

At 3000L the cost of the whole system just doesn't make sense for the returns.

 

Thus I think I'm going to ignore BS8515 and store 7500L from the 54sqm (due to the layout of the pipework, if it is determined that the runoff from the Green roof is not that stained then I can divert at least part of the runoff to my primary RWH tank) and then store whatever is left-over after releasing at the relevant attenuated rate.

 

I'm currently not planning to use a header tank (don't actually have anywhere to put it...)

 

[Blooda]

On 04/09/2022 at 20:54, CADjockey said:

 

This seems like the simplest bit we are installing what with the GSHP & MVHR !

They call it recycling but yes I think it means recirculating the header tank.
https://www.rainwaterharvesting.co.uk/product/rain-director/

 

We have installed that very system, in our self build, When there is no water used for 3 days, it empties the water from the loft tank, and then refills from the Garden Tank.

Ours is 7500l tank, but has attenuation to 1.9l/s.

 

 

 

 

 

[Marvin]

Yes to overcome the dry months you need a store the size of a swimming pool.  The system here is a DIY one and only for loos and garden watering. We use a sand filter to clean the water which once its used for a few days runs clear. We only store about 4m3 in various tanks.

[BristolBuild2020]

On 23/09/2022 at 17:16, Marvin said:

Yes to overcome the dry months you need a store the size of a swimming pool.  The system here is a DIY one and only for loos and garden watering. We use a sand filter to clean the water which once its used for a few days runs clear. We only store about 4m3 in various tanks.

 

I assume your sand filter is before the tank? What does it look like?

 

I might allocate the space for it and add it after the house is built, got enough to worry about at the moment...!

 

 

[Marvin]

1 hour ago, BristolBuild2020 said:

 

I assume your sand filter is before the tank? What does it look like?

 

I might allocate the space for it and add it after the house is built, got enough to worry about at the moment...!

 

 

 

Hi @BristolBuild2020

 

The rain water runs through a catch pit into a big storage tank underground, and is pumped up to the sand filter before draining from their into the cleaner water storage barrels, ready to be pumped for use on the garden or loos.

 

This may help:  https://forum.buildhub.org.uk/blogs/blog/69-rainwater-harvesting/

 

Marvin

[Ferdinand]

Hmmm.

Drought resilience calculation.

 

Is it not the case that we get rainfall even in a drought, so you can extend the resilience period by considering it necessary to supply say 50%? Plus of course usage can always be optimised.

What does that do to your calculations?

F

[BristolBuild2020]

I assume 200L/day during the winter and 300L/day in the Summer.

 

With a 7500L tank, the longest period below 10% capacity is 55 days ending 29th August 1976 and 174 days without overflowing ending 16th Sept 1976!

 

Which ties in nicely with... https://www.countryfile.com/countryfile/great-drought-of-1976-what-happened-and-what-was-the-impact-on-britain/

 

Over the last 130 years the stats are...

 

 

RWH Usage: 11,004m3
Mains Usage: 482m3 

 

Edited October 1, 2022 by BristolBuild2020