Short definition
A faucet aerator is the small unscrewable insert at the tip of a faucet spout. It combines a screen, a flow regulator, and a housing to mix air into the water — giving you a smooth, splash-free stream while metering flow to the rated gallons per minute. When one fixture runs weak and the rest of the house is fine, the aerator is almost always the cause.
What it is
The aerator threads into the end of the spout. Inside the housing sits a flat rubber-and-plastic disc with a calibrated hole (the flow regulator), backed by a brass or plastic screen. Water passes through the disc, the screen breaks it into fine streams, and ambient air is drawn in around the perimeter to aerate the result.
That trio does three jobs at once: it stops the stream from splashing across the bottom of a sink, it traps grit before it reaches a pull-out spray head, and it caps the flow at the rated rate (commonly 1.5 gpm for a WaterSense bathroom faucet, 2.2 gpm for a federal-baseline kitchen faucet).
Standard threads are 15/16″-27 male or 55/64″-27 female on most kitchen faucets, and 13/16″-24 on many bathroom faucets. Cache (recessed) aerators hide inside the spout for a flush look and need a four-prong key to unscrew.
Why it matters to a homeowner
A clogged aerator is the cheapest, fastest, most overlooked fix in plumbing. If your kitchen faucet has slowed to a trickle but the bathroom across the hall runs at full pressure, the supply isn’t the problem — the screen is full of mineral scale or pipe sediment. Unscrew it (counter-clockwise, looking up at the spout), soak it in white vinegar for 15 to 30 minutes, scrub with a toothbrush, blow it out, and screw it back on. Total cost: a dollar of vinegar, or three to fifteen dollars for a replacement.
When a plumber quotes you for “low water pressure” without checking your aerators first, get a second opinion.
Common failure modes
- Mineral scale clog. Calcium and magnesium carbonate cement the screen shut. Standard outcome of hard water in Spokane and parts of the Eastside. Vinegar soak fixes it.
- Sediment grit. After a water-heater flush or any supply work, every aerator in the house collects sand-sized particles. Clean each one once.
- Missing flow regulator disc. A DIY clean dropped the disc down the drain — flow now exceeds the rating and splashes everywhere. Replace the aerator.
- Cross-threaded after replacement. Leaks at the base of the spout. Back it off and re-thread by hand.
- Corroded housing fused to the spout. A strap wrench (cloth-protected) saves the chrome; metal pliers will scar it.
Washington note
Hard-water service areas — Spokane, parts of Bellevue, Issaquah, and Sammamish on Cascade groundwater wells — clog aerators on a 6- to 18-month cycle. Seattle and most of the Cedar/Tolt-fed system runs softer and clogs more slowly. The Saving Water Partnership (Seattle, Tacoma, Everett, and most regional utilities) has historically offered free WaterSense aerators by mail; check your utility’s conservation page before buying.