Views on large rain water harvesting systems

[ey143]

Can I please have some views from builders and home users on their experience or use of a large (1500+ litres) rain water harvesting system?

I have a fairly large house (project) with 5 or so bathrooms and am on a water meter. Rough cost of water in and out as waste is approx 1.4p per litre I am told. As I also have a very large garden and roof, Was thinking of using the water to feed the toilet cisterns in the house. Cost of materials maybe £2500 plus labour but I'm gutting the whole house anyway.

Aside from pump maintenance issues and colour of water, are there any other issues worth considering? Alternative is a bore hole at maybe £7k cost.

Thx.

 

[RNReindeer]

Check the small details with your water authority.
Some authoities will give a rebate on the surface water waste element from your bill if you have a soakwaway. And it needs to be the whole of the roof, not just part of it.
But that might not apply if you have water harvesting/re-use. Although you'd still save on the water in.


Have you considered/costed the use of a sceptic tank? It would probably cost something like £10k for a tank and leach field to accomodate 5 bathrooms. Then it costs something like £150 every few years to empty the tank.

 

[ey143]

Will check thanks.

I live in NW London and am connected to all the mains etc so septic tank might be a stretch too far. Will check with the council if they offer any rebates.

 

[oldbutnotdead]

Not the council you need to talk to about the water rates- have a look at your water bill, it should be itemised with an element for surface water drainage. I've been looking at this sketch (not such a big house though) but I'm not on a meter so it doesn't really work financially. Doesn't mean it isn't worth capturing the rainwater though, come in very handy next time there's a hosepipe ban

 

[theprinceofdarkness]

The number of bathrooms is not a fact, it is the number of people who use the toilets that count in this case. See the attached metering charges :- http://www.thameswater.co.uk/your-account/566.htm Any way if you are metered, the cost of a low flush toilet is 1.6 -1.9 p/flush. it will take a loong time to get your money back!!
Frank

 

[ey143]

Yes you are correct. Indeed it is the water board and not the council that rebate this money if your roof rainwater does not flows into the drains. Perhaps I meant to ask whether the council gives a sudden rebate for green incentives like this.

theprinceofdarkness,

The cost per flush is 3.6p not 1.9p as you have to account for the return of waste charge, so that was not a price range.

You also make a valid point regarding the number of people and not the number of toilets in the house. My issue is that we are a very small family of two adults and the baby we will grow in the years to come. But I'm also thinking ahead in case we may want to sell the house and a large house with A large family will have higher consumption, this may be a positive selling point. You could argue if you're able to afford a house like that then you do not need to worry about the cost of water consumption. anyway need to do a cost feasibility study.

 

[cjard]

If the materials are 2500, and let's say the labour is 1600 ( I generally work on the premise that any bill in the building industry is between 33/67 and 50/50 labour/materials)
410000 pence

5 people flushing 5 times a day (ie excessive figures imho) at 3.6p is a 12.5 year payback


You might see the ROI sooner if you put that cash into a renewable heating system, insulation etc as that's where the govt grant money is atm

 

[RNReindeer]

anyway need to do a cost feasibility study.

A cost/benefit analysis is OK for a simple either/or decision, and you potentially have several either/or decisions: do nothing, soakaway, rain water harvesting, septic tank, etc.
When considering several alternatives. and taking on cjard's comment, a Decision Analysis is the better methodology. It allows you to feed in all the results of various cost/benefit analyses, together with your assumed probablities, to arrive at a preferred course of action.

 

[ey143]

What do you mean by decision analysis? Cost benefit I understand.

 

[RNReindeer]

It's a way of analysing or assessing various options.
It's too complicated to explain in a post like this and you can buy books or even download software for it.

Basically, you initially define your various options, which might be diagrammatically shown as paths. Each option is analysed with a cost-benefit analysis, or other methodolgy, then a probability factor may be added to provide a quantative vaue for that option. Once all options are similarly assessed you will have the best option. You will probably need a standard value by which to compare each option and cjard's comment possibly povides the comparative value: ROI or payback time.

Bear in mind that often an iterative approach is needed, i.e. at the end your realise that some options could have been better assessed, refined or defined. So you start again, but with an improved awareness of the options. Sometimes, you might add various pobablity factors, such as optomistic, neutral and pessimistic. Or you might add these three factors during the cost-benefit stage for each option, or even for each element in the options. For instance, in the toilet flushing element you might use factors of 0.7, 1 and 1.3 against your predicted water saving estimate.

 

[ey143]

Vaguely brings back some dark memories of one of my MBA classes I wasn't paying attention to.

Are you a hedge fund manager?! You don't sound like a builder. Lol.

 

[Norcon]

If you had RNReindeer as a tutor you would soon lose the will to live.

 

[big-all]

am on a water meter. Rough cost of water in and out as waste is approx 1.4p per litre I am told. .

you have your decimal point in the wrong place
i pay £2 a tonne/1000L in and out and thats 0.2p perL or 5L for1p or or less than 1p a flush
you may pay more but you are out by a factor off perhaps 7 or 5 if you pay £3 a ton

 

[ey143]

If he was a builder I would hire him on the back of that comment alone.

 

[big-all]

am on a water meter. Rough cost of water in and out as waste is approx 1.4p per litre I am told. .

you have your decimal point in the wrong place
i pay £2 a tonne/1000L in and out and thats 0.2p perL or 5L for1p or or less than 1p a flush
you may pay more but you are out by a factor off perhaps 7 or 5 if you pay £3 a ton

did you see my post ??