A glass of tap water that looks milky, then clears a minute or two later, is usually not a serious problem. The trouble is that the same look can come from dissolved air, from grit, or from fine particles that stay suspended, and each one calls for a different next step. This guide shows you how to tell them apart at the kitchen sink before you call anyone.
Run a clean glass test
Use a clear drinking glass, not a tinted or dark cup. Run the cold tap for a minute first so the line has cleared, then fill the glass about three-quarters full and set it on the counter in good light. Watch it for two to three minutes without moving it. Note three things: whether the cloud is spread evenly through the water or sits near the top, whether tiny bubbles rise along the sides, and whether a fine layer of material settles on the bottom.
Air clears and leaves nothing behind
If the cloud fades as bubbles rise and disappears completely, the cause is usually dissolved air coming out of solution when the pressure drops. This is common after water has sat in a pipe, after a pump has started, or after work on the supply line. Air-caused cloudiness clears within a few minutes and leaves no deposit on the glass. To confirm it, run the tap longer, then fill a fresh glass. If it stays clear once the air has had time to escape, you have your answer.
Grit settles and leaves a layer
Sediment behaves differently. The cloud drops toward the bottom, and after a few minutes you may see a fine layer of sand-colored or rust-colored material on the base of the glass. Water carrying this kind of grit does not clear on its own, because the particles are heavy enough to settle but too slow to leave the water quickly. Check the next few glasses, not just the first. If grit shows up only on the first draw of the morning, the pressure tank or the line near it may be the source. If it shows up on every draw, the source is more likely upstream.
Compare hot and cold
Fill one glass from the cold tap and one from the hot tap in the same room, after running each for the same length of time. If only the hot side is cloudy or carries grit, the water heater is the first place to look, since sediment can collect inside the tank. If both sides look the same, the cause is upstream of the heater. Do not assume a hot-only result means a single fix, and do not drain the heater until you have confirmed the pattern on more than one draw.
Check the faucet outlets
Unscrew the aerator at the tip of the faucet and look at the screen. Small bits of debris or mineral buildup can make the stream look cloudy at the outlet even when the water in the line is fine. Rinse the screen, put it back, and fill another glass. If the cloud is gone, the fixture was the cause. Repeat the check at one or two other faucets, because a single clogged aerator is common, while a problem in the supply line usually shows up at every outlet.
Write down when it started and what changed
Before you call anyone, note when the cloudiness first appeared. Record whether it began after a filter was changed, after a pump or pressure tank was serviced, after utility work nearby, or after a treatment unit was added, removed, or adjusted. A cloud that started on the same day as a service visit points to that visit. A cloud that came on slowly and has stayed points to something the supply or the well is doing. Either way, a written timeline is the most useful thing you can give a tester.
When to ask for a test
If the cloud does not clear after a few minutes, or if it leaves a deposit every time, stop relying on the kitchen check. On a municipal supply, call the water provider, ask whether there has been any work or treatment change in your area, and ask whether they can confirm water quality at your meter. On a private well, ask a certified lab to test for turbidity, particle content, and the minerals you suspect. A home test kit can give a rough reading, but it cannot identify which particles are present or where they come from. When you compare providers, ask what the test measures, how the sample is collected, and whether you will receive the results in writing. Until the cause is known, use a different source for drinking and cooking. Our methodology page explains how providers on this site are reviewed, and the provider directory is a starting point for finding someone to test or service your system.