Rainwater harvesting tank

[Happy Valley]

I have a quote for a 3000 litre rectangular tank that does not require concrete to position. We will be using it for washing cars, outside taps, toilets and washing machine in a 160 sq m house with mainly 2 people living in it. Location East Cheshire so NW England (just).

 

Is a 3000 litre tank too excessive and could we get away with a smaller tank?

 

Also any recommendations on suppliers - currently have a quote from Owls Hall.

[Mulberry View]

I can't offer any help on this, but am very interested in it.

 

We have only just become aware of the ability to use harvested rainwater for flushing toilets and washing machines. Any practical views on doing this? Presumably some sort of pre-filter will be needed?

 

I had expected ours would be much bigger than this, but we also want ours to provide water for our large garden.

[markc]

3000 litres sounds a lot but in reality it is only 3 cubic metres.

Harvested water for the garden, washing cars etc. is great, i do have reservations regarding its use around the house, maybe someone can answer my concerns regarding standing bacteria and algae etc. is this likely to be a problem in cisterns and washing machines? 

[Happy Valley]

The quote that I have includes the following:

 

1. Leaf removal
2. Particle removal
3. A 3 stage filter including carbon filter 

This allows use for toilets

Edited May 5, 2021 by Happy Valley

[Thorfun]

I thought these tanks were sized according to the roof collection area? at least ours has been. it has to, apparently, be sized so that it overflows occasionally so as to 'recycle' the water some times so you can't size it too big.

 

I got quotes from rainwaterharvesting.co.uk and Rainharvesting Systems Ltd and both were pretty comparable in price but I prefer the look of the F-line tank gravity system from rainwaterharvesting.co.uk so will, probably, end up going with them. haven't bought anything yet though so cannot comment on the company but have been very helpful during the quote stage. both suggested between 4,500litres and 5,000 litres systems for our roof size. 

 

Also, as we've got sedum roofs we have had to keep the drainage from that out of the RWH tank as well as any water from ACOs.

 

hope this helps.

[saveasteading]

I have had 2 RWH systems installed, both for new office blocks. as one was for ourselves I can report in some detail.

1,000m2 office with 30 ish persons average

 

The positives. 

The capital cost was expected to take 10 years to recover, but it was more like 4.

This was because we bought hardly any water, with mains water  being only for kitchens and showers. Bill was about 60 pounds (pound key not working, so now#) per annum including standing charges. in other words hardly any water. standing charge was reduced because we could use minimum pipe dia in.

Also, sewage rates are based on purchased water consumption

if you have mains too, then it will never run out, as it fills the last 10% automatically (check spec)

 

some harvesters have a system that takes away 10% of the water to flush away leaves. we instead had a settlement manhole befre the harvester..

100% of the roof water went to the tank.

the roof was metal so none soaked into tiles.

nobody ever questioned the water quality. it was utterly clean to look at.

 

Negatives.

capital cost.

uses electricity to pump the water into the system

pump will wear out.

doubling up of pipework to carry rain/mains water to different appliances.

If the pump fails, it is your own problem to resolve.

if there is a power cut, you have no water, unless you add header tank.

 

Size of tank. ours was huge (10m3 I think). this was on the upper side from forecast, but meant that it sufficed for a month of no rain. Depends where you live.

For a single family, you may be able to control and reduce use in a long dry period.

A  bigger tank is not necessarily much more expensive. 

But if you have mains, you will never be short)

 

Treatment. For toilets, garden, outside tap it requires no treatment. 

For sinks, taps, basins, showers, bath you have to use mains, or fit filters and UV.

 

Is it worth doing? I will have no choice on a remote farm conversion.

Otherwise there are lots of sums to do.

 

[saveasteading]

1. Leaf removal
2. Particle removal
3. A 3 stage filter including carbon filter 

This was all done by our pre-settlement tank.

A standard manhole with pipe in high and out low, but not bottom.

A leaky bulkhead across the middle, so that water settled in the first half, and particles floated or sank.

After 3 years, it was still not worth cleaning out.

All rwp had bottom grilles to catch leaves. 

No wastage, and no filters, but took up space and had a cost.

[Bitpipe]

I looked into RWH to feed internal systems and saw all of the cons raised above, you do need quite a bit of kit to meet WRAS requirements.

 

There are some concerns over bacteria and virus from bird droppings being washed from roof into your system and not filtered out due to their microscopic size. RWH systems do not typically have UV treatment etc as the water is not intended to be potable. However flushing a toilet will generate an aerosolised spray which could introduce these into the air. 

 

We built a 4000 l tank using IBC in a covered location next to our basement and use it for garden watering only. Helped towards our water calculation signoff.

[saveasteading]

Interesting, Bitpipe

 

Bird  droppings and aerosol. My instinct is that they are not greatly hazardous to us, most should drop to the bottom,  any getting through is dissolved  in 3000 litres then served in 3l flushes, so it will be an insignificant risk. But interested to hear otherwise.

 

From too many experiences of inspecting gutters, it looks as if most of the muck will sit in the gutter and not reach the downpipes.

 

It doesn't look as if UV treatment is too expensive, but that is only from a quick look on-line.

 

I once used IBCs for SUDS on a rather large industrial project, because we could not dig because of contaminants. 5 IBC tanks linked together with tank connectors, and  a single outlet.

 

This was actually as flood prevention as we left the tap open, to dribble away over a few days. Compared to the planner's and Environment Agency preference of sedum roof and harvesting tanks, it saved our client many thousands. 

It is far from pretty, but well suited to that Dagenham industrial estate.

Of course they can be used as cheap harvesting instead. Our client chose not to.

 

Second hand IBC cubes are cheap, and just need an overflow, but may have nasty chemicals therein.

Edited May 5, 2021 by saveasteading

[Simon R]

Just a little to add to the topic. We have 4600L Kingspan Klagester rain water harvesting system which we installed primarily to take care of surface water as the cost of connection to the surface water drain was prohibitive. The system cost £1789 back in January 2019. The system has a few benefits over just a straight tank and pump solution, allowing levels to be monitored and also top up from mains water if required. We use the water for the washing machine, to flush toilets and the garden. It looks and smells like clean water. The tank has a leaf filter, we also added scotch brite mesh filters to the down pipe drains. Keeping light from the water is pretty fundamental and I would not go the IBC route myself.

 

On the minus side. We didn't have a good experience with Kingspan as our pump was found to be faulty but was deemed out of warrantee which is just one year from delivery, We didn't commission the system in the first year of our build! The pump has been replaced with a better one from Divertron which cost less than the £300 service charge that Kingspan wanted just t look at the problem. A bonus from the pump swap is that the pump has a float intake so water is taken from the tank surface rather that the bottom of the tank where sediment will inevitably build up.

 

[Adsibob]

I'm currently considering this.

 

We have to install at least one tank and pump as our extension is too far from the sewer and BCO has insisted on it. That cost of that is about £1200 plus VAT. Architect said if we are going to do that (and we don't have a choice) then we might as well install an additional pump and set up a proper harvesting system.

 

Quote for two pumps and a 3000L tank, supply only, is £3,200 plus VAT. Not sure why it is so expensive. This will enable us to use rainwater from our roof and ACOs in toilets and appliances. So it's an additional £2000 plus VAT to get the water saving and environmental benefits or reusing the water collected as opposed to just sending it to the sewer.

 

I'm struggling to justify it as I think it will take me 15 years plus to recoup that additional £2400 in water savings, and I'm sure in that time I will have to replace the pumps, which I am struggling to understand why they are so expensive. The quicker than expected return on @saveasteading's set up sounds like it might be because it was used in an office block. I imagine there most of the use is toilets, which probably get a lot of use and therefore provide an opportunity for lots of savings. But in our case, most of our use will be for showers and baths, with toilets and appliances being secondary. And as I'm not willing to install the tech required to sanitise the water for showers and baths, I just can't see us saving more than a £160 or so a year, but maybe I'm doing my sums wrong.

 

Been quoted £600 for one with a battery back up in case the power supply is cut off. Not sure that is essential, but I guess if there was a storm with lots of rainwater, that would be a bad time for your power to go.

 

@Simon R I'm interested to know which model Divertron pump you went for which cost less than the £300. I'm being advised to install a £600 pump, which just seems obscene.

[saveasteading]

On 05/05/2021 at 19:45, Simon R said:

our pump was found to be faulty

Had the same issue with another big name supplier. They were very unhelpful. Also, they didn't stock that pump any longer either. I think they are out of that market now.

[Simon R]

18 hours ago, Adsibob said:

I'm interested to know which model Divertron pump

it's the Divertron 1200x, Anglia Pumps have it at £227 which surprisingly is less than the 235 I paid quite a while back.

We would not have gone the rain water harvesting route if we had had the option of a mains connection. In our case the surface water connection was prohibitively expensive. For a private dwelling rain water harvesting systems save no carbon and give you additional maintenance.

[JOE187]

I fitted on of these for a  customer last summer shallow dig tank,  pump and filter pipe included pea shingle back fill should be every thing you need other than change over system at WC.

 

https://www.tanksforeverything.co.uk/Hydrostore-Garden-Harvest-2900GH-Rainwater-Harvesting-Tank?language=en&currency=GBP&gclid=EAIaIQobChMIhqb93uDk8QIVCLrtCh3C3A81EAQYASABEgI3TvD_BwE

[JOE187]

 Also this price includes delivery!!

[puntloos]

So if you're already digging a foundation, would you put the tank under the house? Or under e.g. the terrace? Middle of the garden?

I imagine terrace might be easiest to service?

[Vijay]

Not sure that would be a good idea cos of any maintenance surely?

[SteamyTea]

My water and sewage costs about £8/cubic metre.

City of London costs £1.10

Their shit can't smell.

 

Please don't bring dogs to Cornwall, I am paying to clean the mess up.

[dnb]

On 14/07/2021 at 15:38, Adsibob said:

I just can't see us saving more than a £160 or so a year, but maybe I'm doing my sums wrong.

 

You aren't as far as I can see. And I think you are on the optimistic side at £160, but my maths is based on having a guess at sewerage and surface water costs since I don't have mains drainage.  I am building "for but not with" on the rainwater recycling. The house will support it with a header tank for rain water in the attic and space for pumps etc to fill it from an underground tank, but there will be no underground tank until they get to a sensible price. I am unwilling to pay more than I spent on a treatment plant on something much simpler when it doesn't have a realistic payback time.

[puntloos]

It sounds like the cost of sinking a tank if you already are digging up your garden is almost zero (2000ish quid maybe, based on this tank - 1500 quid incl delivery) but I don't know if the plumbing gets a lot more complicated?

[joth]

7 hours ago, puntloos said:

It sounds like the cost of sinking a tank if you already are digging up your garden is almost zero (2000ish quid maybe, based on this tank - 1500 quid incl delivery) but I don't know if the plumbing gets a lot more complicated?

Don't forget to factor in the cost of carting away the displaced earth, that was the largest component in our quote 

 

Plumbing is more complex, especially to keep within WRAS rules, but ongoing maintenance is what adds up more as you have various filters to clean/ change and invariably some matter gets into toilet cisterns that needs cleaning out from time to time. (our plumber only had bad things to say about the overhead this adds)

Obviously if just using it outdoors, for garden & car/bike cleaning it's much simpler on both fronts. 

[Dan F]

On 05/05/2021 at 14:48, saveasteading said:

This was all done by our pre-settlement tank.

 

Which suppliers provide pre-settlement tank?  Quotes I have don't include this and strongly advise not using water from sedum roof or patio, which is a bit of an issue given only put one set of drainage in.

[saveasteading]

DanF.  I don't think suppliers do presettlement tanks as such:  it is just a watertight manhole or tank, and I designed our own. I thought it was a waste that harvesters diverted 10% of the rain to shed leaves.  In ours, nil rubbish or silt  reached the cisterns.

Sedum or other green roof retains water so reduces harvester quantity. Therefore i disagree with the logic of sedum being priority over harvesting. Agreed avoid sedum filtered or patio water to harvester: much too interesting contents.

How sustainable is a green roof is another topic altogether.