Periodically flushing out the lime and other sediments in the water heater tank improves the heater’s efficiency and lifespan. In neglected water heaters, sediment can accumulate and calcify, making it difficult to remove. Most homeowners should flush their water heaters every six months or so, but if you have extremely hard water, you may want to do it more often. Flushing your hot water heater could be necessary as often as every few months depending on the mineral content of your local water supply.