Your plumbing system may have hundreds of different valves. But
knowing where just one is can prevent thousands of dollars of
damage in a home. The main water valve controls the flow of all
water into your home and must work properly to prevent damage.
First, find the valve. It's usually at the lowest level of your
home near the street. Next test the valve to see if it turns
off. Last, label a large tag with the words main valve and hang
it from the valve handle to make sure all members of your
household can find it before a flood sets in.