Begin by confirming the scope of the issue. Go to every faucet, shower, and tub in your home. Turn on the hot water and observe its pressure. Then, turn on the cold water and compare. If the hot water pressure is noticeably lower than the cold water pressure at all fixtures, the problem is systemic and likely originates at the water heater. If the problem is only at one fixture, you should first try cleaning that fixture's aerator or showerhead before proceeding with these steps.

Locate your water heater. It's typically in a basement, garage, or utility closet. Identify the cold water inlet pipe, which is usually at the top of the tank and may be labeled or marked with a blue ring. Follow this pipe to find its shut-off valve. Ensure this valve is in the fully open position. For a lever-style ball valve, the handle should be parallel to the pipe. For a circular gate valve, it should be turned fully counter-clockwise until it stops.

Before draining the tank, you must shut off its power source for safety. For an electric water heater, go to your home's main electrical panel and turn off the corresponding circuit breaker. It is often a double-pole breaker and should be clearly labeled. For a gas water heater, locate the gas control knob on the unit and turn it to the 'PILOT' or 'OFF' position. Next, turn off the cold water supply valve that you just inspected in the previous step.

Attach a standard garden hose to the drain valve located at the bottom of the water heater tank. Run the other end of the hose to a safe drainage point, such as a floor drain, utility sink, or outside. To prevent a vacuum from forming and to help the tank drain, go to a faucet inside the house (preferably on a higher floor) and open the hot water side. Finally, open the drain valve on the water heater. You may need pliers if the valve is stiff. Allow the tank to drain completely.

Simply draining the tank often leaves the heaviest sediment behind. To effectively remove it, leave the drain valve open and the hose attached. Briefly open the cold water supply valve for 15-20 seconds to blast water into the tank, which will stir up the sediment at the bottom. Then turn the cold water off and let it drain out. Repeat this flushing process 3-5 times, or until the water running from the hose is clear and free of particles.

Once the water runs clear, close the drain valve securely and remove the garden hose. Double-check that the hot water faucet you opened earlier is still open. Fully open the cold water supply valve to begin refilling the tank. Keep the hot water faucet open until water flows out in a steady stream, without any hissing or sputtering air. This signifies the tank is full. Close the faucet. Carefully check for any leaks around the water heater's drain valve. Only after confirming the tank is full and leak-free, restore power at the circuit breaker or turn the gas valve back to its 'ON' position.

Allow the water heater 30-90 minutes to heat the new tank of water. Once it's had sufficient time, go to the various faucets in your home and test the hot water pressure again. It should be significantly improved and now match the pressure of the cold water. If the pressure is still low, the blockage may be further down the line, in the heat-trap nipples on the heater, or within the pipes themselves, which may require professional assistance.