A ball valve is a form of quarter-turn valve which uses a hollow, perforated and pivoting ball (called a “floating ball”) to control flow through it. The ball has a hole through it, by which the valve opens and closes. When the ball is positioned so that the hole runs the same direction as the passageway, the fluid simply flows through it, and the valve is open. The ball can also be positioned so that the hole is perpendicular to the passageway so that the fluid cannot pass through, and the valve is closed. It is controlled from the outside, often with a handle that is turned back and forth 90 degrees to open and close the valve.

Ball valves are much more durable and reliable than gate valves, and more likely to actually be able to open and close after years in an installation serving a hard-water area. On top of the reliability, the fact they use a 1/4 turn (instead of several full turns) and a quick glance tells you whether it’s open or closed. The cheap plastic drain valve that comes on most water heaters, and even the slightly better faucet-type brass valve that comes with some, can easily clog with sediment buildup and is prone to leaking. Replacing it with a straight-path ball valve will ensure that you can get the water out if you need it, and that if sediment does clog it, you can easily unclog it with a long screwdriver. T