Intact plumbing has static water pressure, meaning that if there is a leak, the water pressure will reduce steadily as water leaves the pipes. A pressure gauge tests the current water pressure. To use a pressure gauge, shut off the water to your home to prevent new water from entering the system. Connect the pressure gauge to your plumbing, using a hose, and then watch the readout for a few minutes or up to an hour. If the water pressure lowers over time, you have a leak.
Not all pipes are plainly visible. Leaks in a hidden pipe can cause higher bills and often, damage is completely undetected. Pipe locators work like a stud finder, with locators for metal pipes that use a magnetic field and locators for plastic pipes that use a simple form of radar. Pipe locators are expensive, but usually available for rent at your local home improvement center.
Hydrostatic test systems can be described as a pressure gauge "on steroids." This professional-grade piece of equipment hooks to your plumbing and pumps air or water into your plumbing to raise the water pressure to a maximum allowed by local ordinance. The gauge then reads the new pressure and checks to see if it remains steady, using the same principles as your pressure gauge. This gear can locate leaks that are too small for a DIY pressure gauge to detect. However, it is expensive and complex. Hydrostatic test systems usually are used by professional plumbers.
Flowing water sounds different from still water in a pipe, a fact anybody who's been in a room next to somebody taking a shower understands. In addition, water passing through a leak sounds different from water flowing normally. A sonic leak detector is essentially a microphone attached to a set of headphones. An experienced plumber can use the sound to determine if there is a leak, and then guide himself to the leak's location.