If you have hard water in your home, the walls inside your hot water heater reservoir tank will eventually be covered with what is called "limescale." This is the result of mineral deposits, made up of lime and calcium, slowly building up over time. If left unattended, limescale will cause your hot water heater to malfunction, reducing its efficiency. Use a heavy application of apple cider vinegar three or four times a year to dissolve the limescale and clean out your hot water tank.
Turn off your hot water heater. Look at the area above the hot water heater to find the water supply pipes. A valve on the pipe is controlled with a lever. Turn the lever counterclockwise to shut off the water supply to the heater. If no lever exists, use an adjustable wrench to operate the valve.
Go to the nearest hot water tap on a sink or bathtub and turn it on. This process is called "venting" and will help you drain all of the water from the tank. Leave the hot water running.
Look near the bottom of the front of the hot water heater and you should see what looks like a spigot for a garden hose. This is the drain valve. Connect a garden hose to the spigot and run the hose to the nearest drain. Make sure there are no kinks in the hose. Turn the valve counterclockwise to open it. Check the end of the hose to make sure water is coming out of it.
Wait for the hot water heater tank to drain completely. The wait time should be around one minute per gallon. Turn off the hot water tap and close the drain valve when no more water comes from the hose.
Look at the top of the hot water tank to find a bolt. This bolt secures the anode rod and will typically have either a hex head or a smooth head. If it has a hex head, use an Allen wrench to loosen it. Otherwise, use a ratchet to remove the bolt. Lift the anode rod from the hot water heater.
Set up a funnel at the opening you just created. Pour 4 or 5 gallons of apple cider vinegar into the hot water heater. Replace the anode rod and secure its bolt. Allow the vinegar to sit in the hot water heater for 24 hours. If the lime build-up is particularly heavy, leave the vinegar for up to 48 hours.
Open the valve on the water supply pipe and let it fill the hot water tank for five to 10 minutes. This will agitate the inside of the tank and loosen up any lime that is still sticking to the walls. Close the valve before proceeding.
Turn on the hot water tap to vent the tank and open the drain valve. Chunks of lime may build up in the hose and keep it from draining the tank. Feel along the length of the hose and squeeze to break up the lime. Allow the tank to drain completely.
Close the drain valve and remove the garden hose. Turn off the hot water tap and open the water supply valve. Wait for the tank to fill for about 20 minutes before turning it back on.