Though basic individual usage is really not the problem, anyways. Households don't use all that much water, and most of it can be returned to the waterways after treatment. Water pricing is much more important for affecting the behaviour of businesses.
Will the government find out how many people live in a certain household and use that to arrive at a "basic personal amount" of water?
It's also not too expensive to err on the safe side and give out a generous personal amount. In the quantities that an individual uses, water is pretty darn cheap.
At the moment Irish Water is a semi state body, but there are large fears that it will be sold off to a private company in a few years, along with the PPS numbers and details of everyone in Ireland.
There was a large demonstration against it last weekend [1]
[1] http://www.thejournal.ie/water-charge-protest-in-dublin-1718...
An acre-foot of water, the amount that some farmers are paying $20 for, is 325,000 gallons. At that price, a typical persons usage would be about $0.20/month. Raising that number by 10x, which is roughly the price San Diego pays for water, each person would be using about $2 of water per month. Even assuming the worst case, that 100% of the water had to be produced by desalination costing $2000 per acre-foot, that would only be $20 per person per month.