There are several ways to check your plumbing for a leak. The most common leak we see is a silent toilet leak. To check for one, put a few drops of food coloring into the tank of the toilet and wait several minutes. If the color seeps into the bowl, you have a leak.
A good way to check if you have a leak somewhere in your system is to do an overnight meter read. You just write down the reading on your meter before you go to bed for the night (make sure no water gets used over night). Then read the meter again in the morning before you use any water. If the number changes, you have a leak somewhere. You can also do this when you are going to be out of the house for the day.
Most of the meters in use today have a flow detector on them. This is a small red triangle inside a bubble located under the numbers on the meter. When you are using water, the triangle spins. If you are not running anything that uses water and the triangle is spinning, you probably have a leak.