If your house is supplied by town water you will have a water meter and control valve in a water meter box at the front of your with a green plastic lid or a rust couloured metal lid (frequently near the left or right hand boundary). Remove the lid of the water meter box and inside you will notice a water meter (dial with a counter on it) and a control valve. The control valve will either look like a garden style tap handle or a lever. Turn the handle/lever clockwise until closed and your water supply will be off.