I've been doing this for years, OK? The most common problems are plumbing, and the first thing you have to do is cut off the water. Do you have any idea of where you water meter is? Go outside right now and find it. Seriously. You may have to dig around a bit, but you'll find a valve, probably brass or bronze, that cuts off the water supply to the house. At some time, you WILL have to turn off the water. This is ESSENTIAL information. This valve will be of the type known as a BALL VALVE. The handle part indicates the status of the valve. If the handle is in line with the pipes, it's open. Crosswise to the direction of flow means that it
s closed. Pretty intuitive, really. Block or open. The next thing to do is to find the cut offs for each pipe.
this may seem backwards. Most problems are on the drain side. But unless you have a very new house, or a really diligent plumber, you're going to have really bad cutoff valves. You want to replace them with ball valves.
Why am I making such a big deal of this? Because ball valves stay clean, they don't require washers, and they're specified for two thousand operations open and close and pressure tested for about five thousand pounds per square inch . And they're about a dime per unit more expensive.
Lemme put it this way: thirty years of ball valves and zero failures.
You don't have to do them all at the same time, but every time you turn off the water to the house, check it out.