We have standpipes dotted about the allotment site (roughly 4-6 full size plots share a tap) which is switched on after the 5th April and turned off after bonfire night (we are allowed one bonfire a year on the Saturday of Bonfire Night - the availability of the water is a just in case ....) The water rates depend on plot size so there's obviously a calculation, roughly half the price of rent. So my rental is about £60 for a full size plot plus about £30 for water = total £90 pa.
Rental doesn't seem to get you much - a plot, no toilet facilities, no free compost or bark chippings or manure, the track round the site is in total disrepair. However, the council cover several allotment sites and rent goes towards things like security fencing, new heavy duty padlocks and keys etc which costs £1000s, plus disposal of waste (clearance when a tenant finishes and leaves a plot in a mess etc) - the budget tends to favour whatever is needed urgently at which site rather than what we'd all like.
Water usage - we are allowed to use hose pipes but during peak times especially evenings during hot weather, it is courteous (but not a rule) to allow people to fill water cans - anyone hogging the standpipe with a hosepipe would probably have a riot on their hands. I prefer to go to the allotment very early in the morning when it is quieter. Sprinklers are not allowed which I whole heartedly agree with, but I often see some that have obviously been left switched on overnight.
Water butts - with access to pipe water, you'd think there was no need to get yourself a water butt, but during hot weather and peak tap demand it is very handy, and more so if March is mild and dry (water is only switched on after the 5th April and NEVER before) so worth filling up before the taps are switched off for the winter break (this is to protect the pipe work in case of bad winter weather) There's also the risk of impending hose pipe bans during drought conditions (we were very close to one this year ...) so worth setting up a standby