JayG is correct, we have contacted UU and they have clarified an allotment does not come under the domestic ban, however as a site we will introduce a hose pipe ban as in using a hosepipe to water, we are permitting to fill water butts, watering cans via a hose and those who are less mobile may use the hosepipe to fill they cans nearer the veg it self, the idea is less water is used and it is more direct.
Your site may adapt a similar policy to ours.