Metered water - how much do you use?

We have a brand new allotment site, which is a field divided up into 30 plots measuring 50 feet x 20 feet. There are also 4 half-plots.

Plot-holders are encouraged to have sheds and waterbutts.

We're fundraising for a water supply. A borehole/well is too expensive, but a few troughs on a metered supply is possible. But we need a rough idea of how much water we're likely to use before we can apply for the funds. Which is where I start banging my head, because as we haven't had a summer up there yet, I have no idea how efficiently we can use water. Arrrgh!!

So...
1) Are any of you on metered water supplies?
2) If so, how much does your allotment site use?
3) It would be really useful if you also say how many plot and how big the plots are.

Thanks!!

What's the cost of a borehole?

We looked at boreholes and it's much cheaper to get a mains pipe put in, but I need to figure out how much we'll use before I apply for the funding. Impossible, I know