Finding grit in a glass of tap water is unsettling, but the particles themselves often point to where they came from. In St. Louis, the source is usually either the street supply, the water heater, or something inside a single fixture. Work through the steps below in order, and write down what you see as you go.

Step one: Look at the sample closely

Fill a clear glass from the cold tap and let it stand for a few minutes. Sand and heavy grit usually settle to the bottom quickly. Rust flakes may settle slowly and leave a faint orange tint in the water. Fine material that stays suspended and clouds the water points more toward a disturbance in the supply than to a single fixture. Pour a second glass from the hot tap and compare them side by side.

Step two: Test one faucet at a time

Check the cold kitchen tap, the cold bathroom tap, the hot kitchen tap, and the hot bathroom tap. The pattern is the most useful clue you will get.

  • If grit shows up on every cold tap in the house, the problem is most likely in the supply, either from the utility line or from the main that feeds your home.
  • If grit shows up only on hot water, the water heater is a strong suspect. Sediment collects at the bottom of the tank, and it can be stirred up when the heater runs hard or when the tank is drained.
  • If grit shows up at only one fixture, the cause is most likely that fixture, such as a clogged screen, a worn cartridge, or debris trapped in its supply line.

Step three: Run a white cloth test

Hold a clean white cloth or a coffee filter over a bucket or sink, then run cold water through it at a moderate flow for a short time. Lift the cloth and look at what it caught. Dark specks and fine particles may come from debris in the pipes or from worn rubber parts. Reddish-brown material suggests iron corrosion. Tan or white crusty grit that breaks apart when pressed is often mineral deposit. Note the color and texture, since they help you decide what to do next.

Step four: Inspect the aerator and screens

Unscrew the aerator from the faucet tip and look at the small screen inside. Rinse it under running water and check for trapped grit. If the screen is clogged while the rest of the house runs clean, the aerator may be the entire answer. Also check any screens in the shower head or any inline screen on the supply line at that fixture.

Step five: Check any filter in the line

If your home has a sediment filter, open the housing and look at the cartridge. A dirty or old cartridge can release material and can also let grit pass when it is worn or damaged. Note the date it was last changed, and follow the manufacturer's directions for replacement and for reinstalling the housing correctly.

When the cause points to the street

If grit appeared suddenly on every cold tap after roadwork or a main break in your part of St. Louis, contact your local water utility. Ask whether work was done nearby, whether the lines were flushed, and whether they have recent results for your area. Give them the date you first noticed the problem and a description of what you saw. Most of the time, grit from the supply clears within a short period of running water, but keep watching if it does not.

When a lab test makes sense

Visual checks can tell you where grit is coming from, but they cannot tell you what it is made of or what dissolved substances may be in the water. If the grit keeps returning, if the water also has an unusual color, smell, or taste, or if you simply want a clear answer about the material, a certified lab can test for specific substances. Ask the lab what each test measures before you order it, so you know what the results will and will not tell you.

What to write down before you call anyone

  • The date you first noticed the grit and whether it has come back since.
  • Whether it appears on hot water, cold water, or both.
  • Which fixtures are affected and which are clean.
  • The color, texture, and whether the particles settle in a glass.
  • Any recent work on your street, the water heater, or the plumbing in your home.

A careful record makes it much easier for a plumber, the utility, or a lab to help you quickly. Start with the pattern across your faucets, and the source is often easier to identify than it first appears.