Earthy odor when water first runs

Quick Answer:

An earthy or musty smell only when you first run the water after a period of non-use is usually caused by organic matter or bacterial growth in stagnant water in pipes, tanks or fixtures. Do simple checks and collect a first-draw sample plus a five-minute flush sample to compare. If the smell persists, or if you’re concerned about health, contact your water utility or a licensed plumber for testing and treatment.

Why This Happens

• Stagnation: Water left standing in household pipes, a pressure tank, or a water heater overnight can allow bacteria or organic compounds to concentrate and produce an earthy odor.
• Biofilm and sediment: Small accumulations of biofilm, rust or organic sediment inside a fixture, aerator or section of pipe can release smell when disturbed by the first flow.
• Source water: Natural compounds such as geosmin in groundwater or surface water can create an earthy smell that is more noticeable in the first draw before fresh mains water replaces stagnant water.
• Appliance or location-specific issues: If the smell shows up only at one fixture or only in cold water, the problem is likely local to that fixture, pipe run or supply line; in those cases check the respective fixture—if it’s limited to the kitchen sink, see the note on Moldy smell only at kitchen sink, and if it’s limited to cold taps, see Moldy smell only in cold water.

Step-by-Step What to Do

Step 1 — Confirm where and when it happens

• Test multiple taps (kitchen, bathroom, outdoor spigot) and both hot and cold. Note whether the smell appears only on first run after several hours of non-use.
• Write down which fixtures, and whether hot, cold or both are involved.

Step 2 — Collect samples: first-draw and five-minute flush

• First-draw sample: Without running the tap, collect the very first water that comes out after several hours of non-use (overnight is typical). Use a clean glass or sample container, label it with location and time.
• Five-minute flush sample: Run the same tap continuously for five minutes and collect a sample after those five minutes. Label it separately.
• Store samples in the refrigerator if you will deliver or arrange pickup for testing, and take notes on smell intensity and any color or particles.

Step 3 — Inspect fixtures and simple fixes

• Remove and inspect aerators and strainers for debris or black/green film; clean with soapy water and a scrub brush.
• Flush lines by running each tap for several minutes and check if the smell fades in the five-minute sample compared with the first-draw.
• If the smell is only in hot water, try flushing and checking the water heater’s sediment and anode rod condition (see when to call a professional below).

Step 4 — Decide on testing or treatment

• Compare first-draw and five-minute flush samples. If smell is present only in first-draw and disappears after flushing, the issue is likely stagnant water in a short run or fixture. If smell persists after flushing, further testing or treatment is needed.
• Contact your water utility or a certified lab to test for bacteria, organic compounds and metals if the odor continues or you suspect contamination.

Step 5 — Follow-up actions

• For local fixture issues, replace or deep-clean the affected components (cartridges, hoses, aerators) or the flexible supply line.
• For system issues (well, pressure tank, or municipal supply concerns), follow utility or professional advice for disinfection, tank flushing, or more extensive plumbing work.

What Not to Do

• Do not assume first-run odors are harmless. A smell can be a warning of bacterial growth or contamination and should be checked.
• Do not pour bleach or strong chemicals into plumbing fixtures or the water heater without professional instructions; improper use can damage the system or create health hazards.
• Do not ignore recurring or strong odors — avoid drinking or cooking with water that smells noticeably earthy until you’ve collected samples and ruled out risk.

When to Call a Professional

• If the earthy odor persists after flushing and fixture cleaning.
• If the odor appears in both hot and cold water throughout the house (suggests a source beyond a single fixture).
• If you detect discoloration, particles, or anyone in the home has gastrointestinal or other unexplained symptoms after consuming the water.
• If you have a private well and notice changes in taste or smell, contact a licensed well contractor or your local public health department for testing and well inspection.

Safety Notes

• Avoid tasting water to judge safety. Smell can indicate contamination even if the taste seems mild.
• When collecting samples, use clean containers and label them. If you’re uncertain how to collect samples for a lab, ask the lab or your water utility for instructions.
• Keep children and pets away from any water you suspect is contaminated until the issue is resolved.

Common Homeowner Questions

• Is it safe to drink water that smells earthy only on first run?
  Not until you’ve confirmed it’s only from short-term stagnation; avoid drinking the first-draw and collect samples for comparison or testing.
• Will flushing the tap fix the problem?
  Flushing can temporarily remove stagnant-smell in many cases, but it doesn’t fix underlying sources like biofilm, a contaminated tank, or well issues.
• Could the water heater cause the smell?
  Yes—if the odor is only in hot water, sediment or bacterial growth in the heater can be the cause; call a professional if flushing the heater doesn’t help.