A weak stream is a clue, not a pressure reading
Call it a “weaker stream” unless pressure has actually been measured. The EPA’s WaterSense at Work faucet guidance treats checking a faucet’s flow rate (timing how long it takes to fill a container of known volume) and testing a system’s water pressure as separate checks. That guidance is written for commercial buildings, so use it only for these basic ideas.
Possible restrictions, and normal design
The same EPA guidance recommends periodically inspecting faucet aerators for scale buildup so flow is not restricted, and cleaning or replacing them if needed. The Philadelphia Water Department’s main-break page explains that pipe replacement or repairs to water service near your home can let sediment and debris into your pipes, that faucet aerator screens can trap that debris, and it advises clearing faucet screens. Recent street work is useful background for a plumber, not proof of the cause.
A lower flow may also be by design. The EPA’s bathroom faucet page describes WaterSense labeled faucets and aerators as water-efficient fixtures. Separate “this faucet has always run softer” from “this faucet suddenly got weaker.”
Note a few things without taking anything apart
Using only the normal handles, note whether the weak stream happens on cold, hot, or both, keeping your hands away from hot water. Note whether the change was sudden or gradual and which other faucets still seem normal. Look for visible buildup at the spout and, where easy to see, moisture under the sink. Do not force a stuck aerator, turn unfamiliar valves, disconnect supply hoses, or open the faucet; the EPA notes some faucet accessories need special keys to remove. Leave disassembly and supply-side work to a plumber. A photo can help, as described in what photos help with a home repair estimate.
Give the plumber a focused problem statement
For example: “The upstairs bathroom faucet got noticeably weaker last week. Cold flow seems normal, hot is weaker. Other faucets are unchanged. I have not adjusted valves or removed parts.” Use only details you actually observed. The Building America Solution Center’s guide to leaks in water-using fixtures notes that kitchen and bathroom faucets have separate hot and cold connection hoses and valves, so ask whether the inspection should focus on the aerator, the faucet, or one of those connections, and what check supports the proposed repair. More plumbing questions are on our plumbing page.