Plumbing follows the basic laws of nature -- gravity, pressure, water seeking its own level.
Knowing this, you can understand its "mysteries" and make dozens of fixes to your home's plumbing system. You can save yourself time, trouble, and money! The plumbing system in your home is composed of two separate subsystems. One subsystem brings freshwater in, and the other takes wastewater out.
The water that comes into your home is under pressure. It enters your home under enough pressure to allow it to travel upstairs, around corners, or wherever else it's needed. As water comes into your home, it passes through a meter that registers the amount you use. The main water shutoff, or stop, valve is typically located close to the meter.
In a plumbing emergency, it's vital that you quickly close the main shutoff valve. Otherwise, when a pipe bursts, it can flood your house in no time. If the emergency is confined to a sink, tub, or toilet, however, you may not want to turn off your entire water supply. Therefore, most fixtures should have individual stop valves.