If only one faucet has weak flow, the problem is usually at that fixture—the aerator, shutoff valves, cartridge, or supply lines—rather than the whole house. Comparing hot and cold flow helps narrow the cause without unnecessary disassembly.
Compare the faucet with other fixtures
Run another nearby fixture and compare the flow. If the whole home has lost pressure, stop focusing on the aerator and consider the supply, a whole-house filter, or the pressure regulator instead.
Clean or temporarily remove the aerator
Mineral scale and debris collect in the screen at the faucet tip. Remove it carefully, see whether flow improves without it, and clean the parts while keeping small washers and screens in their original order.
Compare hot and cold flow
If only one side is weak, the restriction may be at that shutoff valve, supply hose, or the faucet cartridge. If both hot and cold are weak, the aerator or faucet body becomes more likely.
Do not force old or seized shutoff valves
A shutoff valve that will not move can begin leaking if forced. If you need it closed to continue troubleshooting and it is corroded or seized, repair that valve first or arrange plumbing help.