Low water pressure in the whole house usually comes from one of five places: a main shut-off or meter valve left partly closed, a failing pressure-reducing valve, a problem on the city’s side, old galvanized pipe narrowed by corrosion, or a hidden leak on the supply line. A few quick checks tell them apart.
Start outside the house. If the neighbors have weak water too, call the water utility; Texas rules require public systems to be designed to hold at least 35 psi, so a street-wide drop is theirs to fix. Next, make sure the main shut-off and the meter valve are fully open. A valve left partly closed after repair work is a common, free fix.
Then look at the parts you own. A pressure-reducing valve sits on your side of the meter, and when it wears out, pressure drops or swings at every fixture at once. A gauge on an outdoor hose bib shows whether pressure is low before water reaches the indoor pipes. In older homes, galvanized steel rusts from the inside until the opening narrows, often leaving some rooms weaker than others.
Rule out a leak early. Turn off every faucet and appliance and watch the meter; if it still moves, water is escaping between the meter and your fixtures, in the yard line or under the slab, and finding it takes professional leak detection. A break on the water line from the meter to the house is the homeowner’s to repair.
These checks narrow the cause but do not fix it. Turning up the pressure-reducing valve will not cure a leak or scaled pipe, and low pressure on the hot side only points to the water heater. If just one fixture is weak, the cause is local, like a sudden drop at the shower.