Our water heater was doing something weird. A valve on the side, with a tube running down from it was leaking very hot water onto the floor. We turned off the water to the water heater to prevent a major catastrophe. Replacing an expensive thermostat solved the problem.
Most modern faucets have the breakable parts (valves and washers) in a replaceable “cartridge”. The best place to get replacements is directly from the manufacturer. Some manufacturers, like Price Pfister, warrant their faucets for life to the original purchaser, and consider you the original purchaser as long as you have the owners manual. This repair takes a minimum amount of time.