Many of people ignore the instructions the came with their water heater to install a pressure reducing valve and a expansion tank on the domestic water supply. When cold water comes into a water heater and is heated it has to expand, without the expansion tank the water has no place to expand and will build up excessive pressure. Water heaters come with a pressure relief valve set at 150 pounds. This means that the pressure will build up to 150 pounds before it is relieved. This will damage the plumbing system in your house partially your facets, the heating manifolds and valves in your heating system.

Also the lack of an expansion tank will cause a water hammer every time you close a faucet, again this will cause damage to your heating manifolds, valves and your house hold plumbing.

These problems are common to both wells and city water.