This is the easiest of all the
utilities to get going, if you're lucky, because the water company are the worst to turn off the supply. The first thing you should try is simply turn on the
tap and leave it running for a couple of hours, if the water keeps running you have
water (good for you).
Next step is to try the internal stop cock, search around for a little tap or handle on the water supply pipes, this simply requires a few turns to get the water flowing. Keep the water going for a couple of hours again, now you have water (that was easy).
Otherwise you will need to go out on to the street and find the valve, this will be a small rectangular metal flap with a sign on it that reads 'WATER' (surprise surprise) this will probably be within easy walking distance of your front door. Open this flap and you are now presented with two options;
One: A water meter or valve, either of which you simply take turn on.
Two: A deep hole (probably filled with water) at the bottom of which is a valve which you will need a special tool to reach. You can either speak to your local friendly squatters who might have such a tool (it is a LONG T-bar with a hex fitting at the end) or you can keep your eye out for the water company out doing their thing, when you see their head down a hole... wander along and borrow it. This is good currency in squatter circles.
Whatever you do with the water, ALLWAYS leave it running for a couple of hours before you use it just to get rid of the dead water in the system. You want nice fresh healthy water not the bad stuff that has been sitting in the pipes for a couple of years.