Quick Answer:
If your first draw of water after a long absence smells like eggs, it’s usually hydrogen sulfide from stagnant water or bacterial activity in the plumbing or heater. Don’t drink that first-draw water. Start by opening the lowest fixture to push old water out, then flush other taps and toilets until the smell clears. If the odor only comes from hot water or doesn’t go away, get a pro to inspect the water heater and pipes.
Why This Happens
When water sits in pipes for weeks, oxygen is used up and conditions can become anaerobic. That environment lets certain bacteria produce hydrogen sulfide gas, which smells like rotten eggs. The same gas can form inside a water heater or in sediment, so hot-water-only smells are common. If the smell appears mostly when the heater runs, see Odor that worsens when heater runs for more on causes and fixes.
Step-by-Step What to Do
Open the lowest fixture first to dump stagnant water after long absence.
Start at the lowest point in the house (garage hose bib, basement sink, lowest tub). Opening that fixture lets the oldest, most stagnant water drain out first. This prevents the stale water from simply moving to other fixtures and gives a path for fresh water to enter the system.
Next, open higher fixtures and run cold water
After the lowest fixture flows clear, go to sinks, tubs and showers on other floors. Open cold taps fully and run for several minutes until the smell noticeably weakens or disappears.
Flush toilets and run showers
Flush each toilet at least once to replace standing water in the bowl and trap. Run showers briefly to purge lines and showerheads; remove and clean any aerators or showerheads that hold scale or sediment.
Check hot water separately
Turn on hot water taps and run them for several minutes. If the smell is present only in hot water, the heater may be the source. In that case, flushing the heater can help, but if the odor persists consult a professional.
Test and follow up
- If the smell clears, use the water normally but avoid drinking from the first draw until flushed.
- If the smell returns or is very strong, call a plumber or the local water supplier for testing and guidance.
What Not to Do
- Do not drink first-draw water after long absence.
- Do not assume the smell is harmless — avoid tasting water to check it.
- Do not pour strong chemicals into your water heater or drains without professional advice.
When to Call a Professional
- If the smell persists after flushing all fixtures for several minutes.
- If the odor is only in hot water and running hot taps doesn’t clear it — the heater may need service. See Sulfur odor when running shower for related causes to discuss with a plumber.
- If you notice discolored water, pressure changes, leaks, or a gas-like smell (in which case contact your gas company immediately).
Safety Notes
- Avoid drinking or cooking with water that smells strongly of rotten eggs until it’s flushed and tested.
- Ventilate the area if the smell is strong indoors; hydrogen sulfide at household levels is unpleasant but usually not harmful in small amounts — still avoid prolonged exposure.
- If you’re unsure about working on the heater, or if your home uses well water, get professional testing before treating the problem yourself.
Common Homeowner Questions
- Will flushing the pipes always fix the smell? — Often it does for stagnant-water odors; flush the lowest fixture first and run others until clear.
- How long should I run water to clear the smell? — Run each tap for several minutes (about 3–5) or until the odor is gone.
- Is a rotten-egg smell dangerous? — Small amounts are usually not dangerous but avoid drinking the water and get the system checked if the smell persists.
For more related articles, see the Sulfur / Rotten Egg Smell in Water hub.