Edit. Sorry, misread the topic title. I'm on a water meter. Doh. Ignore the bit below, might still be handy for those who are on a water meter.
Claimed £274 last year on my tax return.
Single operator, use about 550 litres a day, so on a HF-5 RO with 65/35 waste to pure is like what, 1500 ish litres total? Work about 3 days a week so comes to about £275/£250 most years.
I've got a water meter on the system so I can work out exactly the cost of just the water, not the sewage as those are two seperate charges for every cubic meter of water used. I also use the meter to know when to change my Fibredyne 10" pre-filter, 38,000 or so litres.
For the outside tap including the van I've got another meter that counts how much water is used, then each year I do a waste water abatement claim, seeing as that water doesn't go down the drain I don't need to pay waste water charge on that. Which I think works out £100 or £150 or so a year you get back from the water board. This is with Thames water, you need to check your own supplier if they've got an arrangement like that.
Hope that helps.