Rainwater harvesting - How do you calculate 'pay off' period?

[Deleted User]

we have an eco house with a rainwater harvesting system, installed as the house was being built. The rainwater is only used for the washing machine and toilets, we use water butts for the garden. Water is automatically pumped up from the tank as needed. We are on a water meter and our yearly bill comes to £190. I think we actually save about £200 a year at most. We would never retrofit a water harvesting system like ours, where the tank is buried below ground. It would not be at all economical

OffGridLiving

Our water bill comes to £792 per annum. According to United Utilities we'd get a £39 per annum rebate if our rainwater goes into the brook (woo!) and if RWH reduced our mains water useage by half (£396) then we would be looking at a total saving of £435 per annum. If the rainwater installation cost us £4350 to install then we'd break even after 10 years. As important is that if our household income drops for any reason, ill health, job loss then our outgoings are just that little bit less each month (£36 per month).

We're looking to retrofit a RWH solution this year and so I'll document the costs and report back.

EricMears

OffGridLiving wrote: »

.......if RWH reduced our mains water useage by half ......

50% could be a tad optimistic. A third is generally accepted figure; I've demonstrated that 37% is do-able and I guess if you include filtration so that you can use water for washing (clothes and bodies) you might improve on that by quite a bit.

However, I'd hope you can install RWH for a lot less than £4350. You'd be very lucky to find quite as much of the system from recycled sources as I did but my £200 should give you something to aim for.

PM me if you need any hints on project.

OffGridLiving

EricMears wrote: »

50% could be a tad optimistic. A third is generally accepted figure; I've demonstrated that 37% is do-able and I guess if you include filtration so that you can use water for washing (clothes and bodies) you might improve on that by quite a bit.

However, I'd hope you can install RWH for a lot less than £4350. You'd be very lucky to find quite as much of the system from recycled sources as I did but my £200 should give you something to aim for.

PM me if you need any hints on project.

I just followed kittie's 50% figure in her post (annual bill is now £190, saving £200), which I then checked against a few other websites. This seems to be a common chart for water useage:



We would plan to use a system that covers WC Flushing, garden & car washing & washing machine, which is 50% of the useage on the pie chart above. I got the £4k figure from various sources as a realistic figure for retrofitting a 'fit and forget' RWH system large enough for a family.

As we are already planning on doing remedial work with the drains, have easy access to our toilet plumbing via a 'riser' that goes up through the building and we're planning some landscaping work in the garden that would require a digger, we would hope to reduce those costs.

jackyann

We too installed a rainwater system from Rain Direct (Peterborough) who are helpful and pleasant.
We chose a 2,500 litre system as we are only 2 adults, but we do find it switches over to tap fairly often. We pay £38 a month for our water - as a new build, we are metered - but I am hoping that it might come down, as Anglian will only estimate once a year and based that figure "on what might be expected".

When making decisions about our self-build, I found the Centre for Alternative Technology a mine of information. They were very practical and level-headed, and I was very grateful to them (yes, I did send a donation!)

EricMears

jackyann wrote: »

. . . . . Anglian will only estimate once a year and based that figure "on what might be expected".

No sure how Anglian carry on but when Severn Trent generate an estimated bill they put the readings they're using on the bills and invite customers to advise them of the actual readings if they don't want to accept an estimate.

rwhexpert

well, you would save around 50% of your water usage, therefore half off your water bill so that really depends on the cost of your system and installation.

Lets take an average Dairy farmer who spends around £12,000 per year on water bills - they would probably spend around 12,000 on a massive rainwater storage tank system and be saving literally half or more on those prior water rate bills...

So the payback rate for a small to average family of 3 would be around 3 or 4 years if the total cost of your water bills are 450 to 500 per year and the system would probably cost you around £2k ish.

zeupater

rwhexpert wrote: »

well, you would save around 50% of your water usage, therefore half off your water bill so that really depends on the cost of your system and installation.

Lets take an average Dairy farmer who spends around £12,000 per year on water bills - they would probably spend around 12,000 on a massive rainwater storage tank system and be saving literally half or more on those prior water rate bills...

So the payback rate for a small to average family of 3 would be around 3 or 4 years if the total cost of your water bills are 450 to 500 per year and the system would probably cost you around £2k ish.

Hi

Welcome to the forum ....

... is the above saving strictly correct ... or even anywhere near correct ??

When you take the fixed charges such as standing charges and surface water drainage (based on rateable value) into account a 50% reduction in metered water usage is reflected as a billing reduction well below 50% for most domestic households. Of course, the more metered water you use, the proportion of cost attributable to the 'fixed' charges becomes less significant ...

Regarding the '£2k ish' .... leaving DIY solutions based on 1tonne IBCs aside, most of the domestic scale RWH kits (2000-5000 litres?) I've seen are well above £2k before delivery, site preparation & installation (eg http://shop.septictank.co.uk/Rainwater-Harvesting/Graf-Rainwater-Harvester-Home-And-Garden-5000-Litre ), so isn't this a little understated ? ..... we had a 'standard' system priced up for us a number of years ago which was well undersized (~1000litre) which would have been closer to ~3x the above cost if we'd been considerably more financially inept than we are and hadn't done a little research first ...

HTH
Z

[Deleted User]

we had the tank cleaned out at the end of summer, as recommended every five years. The company did a great job, pumping out, cleaning and disinfecting, they also flushed out all the tank inlets. The rainwater had been getting coloured and had developed a `bad egg` odour. The cost was around £500 and was money well spent but that was almost 3 years water savings gone. I stand with what I said previously, it is not cost effective to retrofit and sorry rwhexpert, you are talking pie in the sky nonsense re family payback time. I speak as I find ie we HAVE a rainwater harvesting system, one which is maintained and looked after

Cardew

rwhexpert wrote: »

well, you would save around 50% of your water usage, therefore half off your water bill so that really depends on the cost of your system and installation.


So the payback rate for a small to average family of 3 would be around 3 or 4 years if the total cost of your water bills are 450 to 500 per year and the system would probably cost you around £2k ish.

As zeupater above states you have ignored standing charges and Surface water Drainage charges; so 50% is not realistic


However I am just trying to fathom out your arithmetic on payback time. Even in the unlikely event you could save 50% on a £450 to £500 water bill, that is £225 to £250 a year. after 4 years that would be a maximum saving of £1,000 - for a £2,000 system.


Not to mention the maintenance/electricity costs described above. Also even at today's rock bottom interest rates, £2000 invested in a long term account would earn a couple of hundred pounds in 4 years.


In the real world I doubt if it would ever achieve 'payback'.