Water pressure problems are symptoms, not diseases — low pressure can mean anything from a clogged aerator ($0 fix) to a failing main line ($3,000+ problem), and high pressure silently destroys water heaters and appliances. Normal residential pressure is 40–80 psi. This section helps you diagnose which end of the range you're on, what causes it, and the fixes in order of cost.
Diagnose before you fix
A $10 pressure gauge on a hose bib tells you more in 30 seconds than an hour of guessing. One fixture low means a fixture problem; whole house low means a supply problem; pressure that drops when two fixtures run means a restriction or undersized lines.
High pressure is the silent killer
Pressure above 80 psi voids appliance warranties and shortens water heater life. A pressure reducing valve ($300–$600 installed) is cheap protection our water heater guides assume you already have.