Cloudy water looks alarming in a glass, but the glass itself can tell you most of what you need to know. Before you call anyone or buy anything, run a simple check and write down what you see. Cloudiness usually falls into three groups: tiny air bubbles, particles that settle, or material that stays suspended or dissolved. Each points to a different next step.

Run the glass test

Fill a clean clear glass or jar from the cold tap that looks cloudy. Set it on a counter where you can see it, leave it alone for two to three minutes, then look at it from the side in good light.

If the cloudiness clears from the top down, you are seeing dissolved air coming out of solution. Water under pressure holds more air, and when pressure drops at the tap the air comes out as fine bubbles that rise. This is common after pipes have been drained or after work on a pressure tank or pump. It usually settles within a few minutes and is not a sign of contamination. If you see it on the first draw of the morning and it clears fast, air is the likely cause.

If the cloudiness settles to the bottom and leaves clear water above, you are looking at sediment. Grit, rust flakes, or fine sand is moving through the line. Check whether it is worse on the hot tap, which points toward the water heater, or on the cold tap, which points toward the supply or the treatment equipment. Note whether the settled layer is gray, tan, orange, or black, because the color narrows the source.

If the glass stays cloudy from top to bottom after several minutes and nothing settles, the cause is suspended fine particles or dissolved material that is not coming out of solution. This is the result you should not guess about. Do not try to diagnose it from the glass alone.

Narrow it down by location

Run the same test at more than one tap. If only one fixture is cloudy, unscrew the aerator at the tip of the faucet, rinse out the screen, and run the water again. A clogged screen can make the flow look milky. If every tap is cloudy, the problem is upstream of the fixtures: the supply, the water heater, a softener or filter, or the pressure tank on a private well.

Ask whether the change started at a specific time. Work on the well, the pump, the pressure tank, the main line, or the treatment equipment is a common trigger. Write down when you first noticed it and anything that was done to the house or the water system around that time. This record helps whoever you call.

Decide who to call

If the test points to air, give it a day and retest. If it keeps happening with every draw, ask the company that worked on the pump or pressure tank to check the air charge and the pressure settings.

If it points to sediment on the hot side, a water heater flush is a job many homeowners handle themselves, but a plumber or water heater technician can do it and check the anode rod and drain valve at the same time. For cold-side sediment, ask the water treatment company whether their visit includes checking the pre-filter and the supply line, and whether they will test the water before recommending new equipment.

If the water stays cloudy, has an odor, a color, or any change you cannot explain, stop using it for drinking and cooking until you have an answer. Contact your local water supplier if you are on a municipal system, or a state-certified laboratory if you are on a private well. Ask for a test that matches what you saw, not only a general report.

What to ask before you pay for a fix

When a company offers a filter or treatment unit as the answer to cloudy water, ask them to name the test that showed what the problem is. Ask whether the recommendation depends on a lab result or a field check, and what the check measured. A good answer names the cause you saw in the glass and explains how the proposed equipment addresses it. If the answer is only a sales pitch, get a second opinion before you commit.