Begin by turning off the power to your water heater. For an electric model, locate your home's circuit breaker panel and switch off the breaker dedicated to the water heater. It is often a double-pole breaker and should be clearly labeled. For a gas water heater, find the control knob on the gas valve assembly on the front of the tank and turn it from the 'ON' or 'PILOT' position to 'OFF'. This is the most critical safety step to prevent damage to the appliance.

Locate the cold water inlet pipe, which is typically on the top right side of the water heater and marked with a blue ring. Find the shut-off valve on this pipe. It will either be a round, wheel-like handle (gate valve) or a lever handle (ball valve). Turn the gate valve handle clockwise until it stops. For a ball valve, turn the lever handle a quarter turn so it is perpendicular to the pipe. This will stop any new water from entering the tank while you drain it.

Attach a standard garden hose to the drain valve located at the bottom of the water heater tank. Make sure the connection is secure to prevent leaks. Run the other end of the hose to a suitable drainage point, such as a floor drain, a large utility sink, or outside to a driveway. After the hose is in place, go to a sink inside the house (preferably on an upper floor) and open the hot water tap fully. This will allow air into the tank, breaking the vacuum and allowing water to drain out smoothly.

With the hose securely in place and a hot water faucet open, you can now open the drain valve on the water heater. Most plastic valves have a small slot that can be turned with a flathead screwdriver. Brass valves typically have a small handle you can turn by hand or with pliers. Turn the valve counter-clockwise to open it. The hot water and sediment will begin to flow out through the hose. Be patient, as a full 40- or 50-gallon tank can take 30 minutes or more to drain completely. You will hear the popping and crackling of sediment as it exits.

Once the water flow from the hose has slowed to a trickle, the tank is mostly empty. To remove the stubborn sediment caked at the bottom, you will perform a scouring flush. With the drain valve still open, turn the cold water supply valve on for 15-20 seconds, then shut it off. This will blast water into the bottom of the tank, stirring up the remaining sediment and flushing it out the drain hose. Repeat this process 3-4 times, or until the water running out of the hose is clear and free of debris.

Once the water runs clear, completely close the drain valve at the bottom of the tank by turning it clockwise until it is snug. Do not overtighten, especially if it is plastic. You can now disconnect the garden hose. Go back to the cold water inlet valve at the top of the tank and open it fully by turning it counter-clockwise. You will hear water rushing in to refill the tank. Leave the hot water faucet in the house open during this process; it will hiss and sputter as air is pushed out of the lines. The tank is full when you have a steady, air-free stream of water flowing from the faucet.

After confirming the tank is full (steady water flow from the hot water tap), you can safely restore power. Go to the faucet and turn it off. For an electric heater, return to the circuit breaker panel and switch the water heater breaker back to the 'ON' position. For a gas heater, turn the control knob back to the 'PILOT' position, follow the manufacturer's instructions printed on the heater to relight the pilot light, and then turn the knob to the 'ON' position. The water heater will now begin to heat the new tank of water. The popping noises should be gone.