Plumbing is the system of pipes, drains, fittings, valves, and fixtures installed for the distribution of potable water for drinking, heating and washing, and waterborne waste removal.
The term "Plumbing" also refers to the skilled trade which installs and maintains it.

Plumbing equipment includes devices often hidden behind walls or in utility spaces which are not seen by the general public. It includes water meters, pumps, expansion tanks, backflow arrestors, water filters, UV sterilization lights, water softeners, water heaters, heat exchangers, gauges, and control systems.
Specialized plumbing tools include pipe wrenches, flaring pliers, pipe vice, pipe bending machine, pipe cutter, dies and joining tools such as soldering torches and crimp tools.

vCalc's Plumbing folder contains equations that pertain to plumbing.