You should anticipate paying around $100 to have your water heater flushed. Given how harmful sediment may be to your water heater, this is a small price to pay. Flushing your water heater at least once a year is recommended, and you may want to have it done more frequently if you live in a hard water area and do not have a softener. If you have a working softener, you can get away with flushing once every couple of years, but flushing more regularly won't hurt. Your plumber can give you an accurate idea of how often you should have your Belmont home’s water heater flushed.