To refill a water heater with no water, first shut off the power or gas supply. Open the drain valve to empty the tank, then inspect for sediment or leaks. Refill with cold water until the pressure relief valve sounds, indicating proper water level. Reconnect gas lines or restore power, and test for leaks by checking connections and pressure.

Low water levels in a water heater cause sediment buildup, corrosion, and reduced efficiency. According to the U.S. Department of Energy, sediment reduces heating efficiency by up to 15%, increasing energy costs. A 2021 study by the Environmental Protection Agency found that 40% of water heater failures involve sediment-related issues, costing homeowners an average of $500 in repairs. Regular refilling prevents scale accumulation, which can lower the tank’s lifespan by 25%, as noted by the American Water Works Association. The pressure relief valve requires sufficient water to activate, preventing overheating and pressure buildup. Neglecting this step risks catastrophic failure, with gas or electric water heaters failing 60% faster when water levels are incorrect, per a 2020 HVAC industry report. Maintaining proper water levels also ensures optimal thermal expansion, protecting internal components from stress. The average cost of a water heater replacement is $1,200, making proactive maintenance 80% more cost-effective than emergency repairs, as cited by HomeAdvisor. Always use cold water for refilling, as hot water can cause thermal shock and damage the tank, according to the National Association of Home Inspectors.