It should be simple enough to have a baseline allocation, along with an increased price after that's used up. It's also worth noting that water probably doesn'

It should be simple enough to have a baseline allocation, along with an increased price after that's used up. It's also worth noting that water probably doesn't need to be very expensive before usage starts getting curbed quite heavily by the main consumers. If there's no price, might as well use as much as you're allocated - there is no direct consequence for doing so.