Poweshiek Water is a "Closed System" Expansion Tanks are a Critical Safety Device!     This installation shows the use of a thermal expansion lank on a water heater. Water expands when heated; the expanded water creates added pressure in the water heater tank and piping. The expansion tank is a remedy in systems that are "closed" due to a check valve in the water meter pit. Temperature and pressure relief valves are not enough protection to ensure a safe system. Many water heater companies will not warrant their product on a closed system unless there is an expansion tank installed. Poweshiek Water Association recommends the use of an expansion lank. PWA will not be held responsible for any damages that may occur if an expansion lank is not installed or installed incorrectly.   Call your plumber for additional information.