How to lower the water pressure in a normal house?

If you are on city water, there will be a Pressure Reduction Valve where the water pipe enters the house. This is a bell shaped fitting with an adjuster nut on top. Loosen the locknut (top one ) and turn the lower nut anti-clockwise to reduce pressure, then lock it again.

- NOTE - some PRV's will go up in pressure when they get old, and are impossible to reduce any more. In this case you need to turn OFF the water outside and fit a new PRV. They cost around 40-60 depending where you buy them.