So the allotments don't have controle of the water, personally i would try to change that to the allotments having control so the members could decide when its turned on and off, not the council 30% of your income is a lot of money.
Our water is on a meter and at one time was on all year, but then the water bills were not as they are now When big water bills started coming in it was proposed that every one paid £5 extra on their rent and the water was turned off 1st Oct to 1st of May, It was made very clear that if the members did not subsidise the bill then it would be turned of completely, last year it went up another £5 (added to the rent) unanimous vote for the proposal.
Yes there where complaints mostly from people with horse and some that claimed they don't use the taps, the first were told that its the members decision not the committees, the others your paying for it so i suggest you use the taps.
Now we dare not turn the water on a day early nor turn it off a day late simply because the members are having to pay for it.