To fill a water heater reservoir, disconnect the power, inspect the heater, close the relief and drain valves, bleed the pipes, wait for the tank to fill, and restore power to the heater. This procedure does not require tools or supplies.
Shut off the power to the heater, and visually identify its three valves. The water supply valve is attached to the water pipe, one of two pipes at the top of the heater. The metal relief valve is also located near the top, and the circular drain valve knob sits along the lower edge.
Pull the relief valve lever to the "shut" position, and turn the drain valve all the way to the right. Leave the water valve open. Open the household faucets to remove air bubbles from the pipes. Keep the faucets open and the power off. While the tank is filling, examine the drain and relief valves for leaks. Correct leaks by tightening the affected valve. Close the faucets when water gushes out.
Restore the heater's power supply, and wait several hours for the water to heat. Do not touch the heater or its pipes after you restore the power, as the hot water return pipe becomes dangerously hot.