Plumbing is any system that conveys fluids for a wide range of applications. Plumbing uses pipes, valves, plumbing fixtures, tanks, and other apparatuses to convey fluids.[1] Heating and cooling (HVAC), waste removal, and potable water delivery are among the most common uses for plumbing, but it is not limited to these applications. The word derives from the Latin for lead, plumbing, as the first effective pipes used in the Roman era were lead pipes.

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 shut-off, or stop, the 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, like a leak, is confined to a sink, shower, or toilet, however, you may not want to turn off your entire water supply. Therefore, most fixtures should have individual stop valves.