What is Water Hammer? Water hammer is one of the household water-related terms that water users should be aware of to avoid it and know how to handle it. Water hammer is caused by the sudden shutdown of a pipe, causing a sudden change in pressure. A simple analogy is to imagine a person as water and a pipe as a path. If everyone were to walk along, there would be no problem. However, if an object suddenly blocks the path and causes a sudden stop, those walking together wo