If your kitchen faucet in St. Louis suddenly sprays sideways, sputters, or slows to a weak trickle, the small screen at the tip of the spout is a common cause. That screen is called an aerator. It mixes air into the water stream and softens the flow. Over time it can collect mineral deposits, bits of debris from the pipes, or both. Before you assume your under-sink reverse osmosis system has a problem, check the aerator. This is a quick job that most homeowners can finish with basic hand tools.
What the aerator does
The aerator sits inside the threaded tip of the main faucet, not on the separate RO faucet. It contains a fine mesh screen and small internal parts that shape the stream. When the screen gets partly blocked, water still comes out, but the pattern becomes uneven and the flow can drop. This often happens with the main cold or hot faucet, which carries the same water your home uses for washing and cooking. It does not mean your RO filter has stopped working.
Signs it is the aerator and not the RO system
- Only the main faucet is weak, while the RO faucet at the sink deck still pours at a normal pace.
- The stream splits, spits, or sprays in several directions.
- The problem shows up on hot, cold, or both sides, and it may get worse over several weeks.
- Small grit or white flakes appear in the water after you run it for a moment.
If the RO faucet is also weak, the aerator is less likely to be the main cause. In that case, check the RO system itself and the supply shutoff valves before you change any filters.
Simple steps to check the aerator
- Turn off the water to the faucet if your shutoff valves allow it, or work with the faucet off and the tap closed.
- Place a towel in the sink to protect the finish and to catch small parts if they drop.
- Unscrew the aerator by hand. If it is tight, wrap a cloth around it before using pliers, so the finish is not scratched.
- Take the parts apart in the order they came out, and lay them on the towel in sequence so you can reassemble them correctly.
- Look at the mesh screen against a light. If it is covered with white scale or dark particles, it needs cleaning or replacement.
- Rinse each piece under running water. For mineral buildup, soak the parts in plain household vinegar for a while, then rinse them well.
- Reassemble the aerator in the same order, screw it back onto the faucet by hand, and turn the water on slowly to test the flow.
Checks to run after cleaning
Run the faucet on both hot and cold for a short time. Watch for a steady stream with no spitting. If the flow is still weak, remove the aerator again and make sure no small parts are missing or reversed. Then check the shutoff valves under the sink to confirm they are fully open. Look at your home water pressure at a second faucet as well, since a problem across the whole house points to a different cause than one faucet.
When to stop and ask for local help
If the faucet still drips, the aerator threads are damaged, or the water shows a strong color or smell after cleaning, stop and get help from a qualified local plumber or your water provider. Do not force a stuck part. If you see discoloration or sediment in the water across the house, you may want to record what you notice, including when it started and which faucets are affected, so the person who helps you has a clear starting point.
Keep the RO system in its place
A clean aerator often solves a weak main faucet in a few minutes. It is a simple first check that saves time and keeps you from changing RO filters that are not the problem. Once the aerator is clean, return to your normal routine for your RO system, including the filter schedule your system manual lists. Your RO faucet and your main faucet are separate, so keep them separate in your troubleshooting. Checking the aerator first is a practical habit for any St. Louis homeowner who uses both.