In regards to water lines, there is a simple two step test. First a pressure gauge is attached to some valve and the valve is opened. As long as all water use is stopped, the gauge will show the pressure at which water is delivered from the street. The water meter is turned off. The pressure on the gauge will remain constant if there are no leaks. Normally, if a pressure drop is located, faucets, toilets, and other water outlets are rechecked for use that was slow or drips. If such a running toilet, no drips or slow use, is found, then the lines must be leaking under the house.