If you've opted for a tankless water heater in your house, it's important that you keep up with the routine maintenance required to keep it clean and functioning at its best. Here are some tips for cleaning and caring for your on-demand water system to get rid of contaminants. Clean the Inlet Screen Shut down the water flow to the heater, and turn the heater itself off. Then, disconnect the inlet tube to get access to the screen on the inside of the inlet.