Cloudy tap water alarms people because it looks like something is wrong with the water itself. Often it is harmless air. Sometimes it is sediment, and occasionally it is something that needs a proper test. The steps below separate the three before you buy anything.
Run the glass test
Fill a clear drinking glass from the cold tap, set it on the counter, and leave it alone for two or three minutes.
If the cloudiness clears from the bottom up and tiny bubbles rise to the surface, you are seeing dissolved air coming out of the water. Water under pressure holds air the way a sealed bottle holds gas, and the air comes out when the pressure drops. This is the most common cause, and it is not a sign of contamination.
If fine particles settle into a layer at the bottom, or you can see specks drifting down, you are looking at sediment. Sediment is solid material carried in the supply.
If the water stays cloudy and even after it sits, with no bubbles and no settling, the cause is something dissolved or very fine that does not separate on its own. Stop guessing at that point and get the water tested.
Check the pattern before you blame the equipment
Write down a few answers before you call anyone:
Which taps show it: every cold tap, or only one? A problem at one fixture points toward that fixture or its supply line. A problem everywhere points toward the main supply.
Hot or cold: compare the two. Cloudiness only in hot water points toward the water heater rather than the supply.
When it started: note whether it began after street work, a water main repair in the area, or a service visit to a private well pump. Those events often explain the change.
Whether neighbors notice it: if only your house is affected, look at the plumbing on your side of the meter. If neighbors have it too, the problem is probably on the supply side.
Whether it follows a long idle period: water that sat in the lines after a vacation or an empty house sometimes clears in the first few minutes of running.
What to do next
If the cloudiness is air, run the cold tap for a few minutes and wait. Air-related cloudiness usually clears without any action.
If it is sediment, check whether a filter upstream of your fixtures is clogged, and ask your water utility (if you are on municipal water) or your well service (if you are on a private well) whether work in the area could have stirred up material.
If it persists, have the water tested by a certified water testing lab. Before you order a test, ask the lab which parameters are on its panel and whether it covers turbidity, metals, and bacteria. A generic water test may not answer your question. If you are on a private well, include a bacteria test.
Do not buy a treatment system until you know which of the three causes you have. Equipment chosen for the wrong cause often leaves the cloudiness exactly where it was, and the money is gone before the real problem is found.