The farther pipes are from the main water line, the less water pressure there is for fixtures, such as sinks and showers. This leaves bathrooms on upper floors particularly at risk of low water pressure. Two methods ensure there is enough water pressure on upper floors for properly running plumbing fixtures. By making sure the pressure isn't being siphoned off by other devices and increasing the overall water pressure to your home, you ensure there is always be enough pressure in your upstairs bathroom.
Turn off all of the devices inside your home that use water. That includes sinks, showers, sprinklers, dishwashers and washing machines. This frees up available water pressure inside your home.
Run the shower in the upstairs bathroom testing the performance while no other devices are using water in your home. If the performance is adequate, the solution is using the shower and sink when there are no other devices in your home are using water. If the performance is still poor, you must increase the water pressure to the entire house.
Locate the water pressure regulator. The valve is located along the main water line, usually in a plumbing access panel or in the basement.
Loosen the nut on the valve's top with adjustable pliers. This loosens the adjustment screw's hold above the nut.
Turning the adjustment screw clockwise increases the amount of water pressure released to the entire plumbing system in your home. Turn the screw in small increments, checking the performance at the upstairs shower each time until the performance is adequate.
Tighten the nut on the pressure valve after you have set the water pressure at the desired level.