An inexpensive way to discover a leak is to have a flood alarm.  A flood alarm is a very easy to install.  As a matter of fact anyone can install one.  It is easier than a smoke detector,  just put a battery in one and place it on the floor.  If your water heater, sump pump, ac unit or water softener are located in an area of your home where you don’t necessarily have to frequent.  You may want to place one in that space.  This device will let out a siren type sound when water hits the bottom of it’s contacts.  That way you know something is wrong before it causes major damage.