This hub covers sulfur or “rotten egg” odors in water. The smell may be only on hot water, only on cold water, strongest in the shower, or noticeable only at certain fixtures.

These odors often start after a water heater change, an outage, winterization, filter work, or plumbing repairs. Sometimes the smell is strongest on the first draw and improves after flushing.

Use the groups below to match the hot/cold pattern and what changed recently, then open the closest article title.

Related category: Water Contamination, Taste & Odor

Hot-only vs cold-only sulfur smells

Clues based on whether the smell is tied to hot water or cold water.

• Rotten egg smell in hot water

  Smells limited to hot taps usually point to issues inside the water heater such as sulfate-reducing bacteria or reactions with anode rods; treatment often focuses on the heater itself.

• Sulfur smell only in cold water

  Cold-water odors suggest a source in the supply, storage, or a cold-water treatment device rather than the heater.

• Odor that worsens when heater runs

  If the smell intensifies while the heater is operating, heat-driven reactions or bacteria in the tank are likely contributors.

After changes or events

Smell that begins after heater work, outages, repairs, winterization, or installs.

• Rotten smell after water heater replacement

  New or disturbed tanks can release trapped bacteria or cause chemical reactions; the timeline and installation details help identify causes.

• Sulfur smell after city water outage

  Outages and main repairs can introduce sediment or change disinfectant levels, sometimes triggering temporary odors at the tap.

• Sulfur smell after plumbing repair

  Work that exposes or agitates plumbing can release buildup or let anaerobic bacteria into lines, producing a noticeable smell.

• Rotten smell after winterization

  Winterizing or de-winterizing can leave contaminants or introduce stagnant water pockets that smell until flushed or treated.

• Egg smell after installing filter

  Filters can harbor bacteria if not installed or maintained correctly, and some media reactions can generate sulfur-like odors.

• Egg smell after backflow install

  Backflow assemblies and related changes may create pockets of stagnant water or alter flow patterns that reveal odors.

• Egg smell after long vacation

  Extended stagnation in plumbing while away can allow bacteria to develop or trapped water to go bad, causing first-use odors.

Where you notice it most

When the smell is strongest at a specific fixture or use.

• Sulfur odor when running shower

  Showers can concentrate odors through warm water and aeration; localized issues often relate to nearby piping or the water heater.

• Smell only in upstairs bathroom

  Floor-by-floor differences suggest localized piping, branch lines, or water use patterns rather than the main supply.

• Smell only in kitchen sink

  Kitchen fixtures can pick up odors from sink drains, garbage disposals, or undersink plumbing as well as the incoming water.

• Sulfur odor in laundry water

  Laundry odor often results from standing water in machines or supply lines, and it may differ between hot and cold cycles.

First-draw and flushing behavior

How the smell behaves after sitting and after flushing lines.

• Odor only in first water draw

  Smells that appear on the first draw and fade after running taps usually point to stagnation in short sections of piping or fixtures.

• Smell disappears after flushing system

  If flushing clears the odor, the issue may be temporary buildup or isolated contamination rather than persistent source contamination.

Recurring patterns

Smell that returns on a repeating schedule.

• Smell returns every few weeks

  Periodic recurrence can indicate seasonal water changes, intermittent bacterial growth, or regeneration cycles in treatment equipment.

Well-water sudden onset

When well water develops a sulfur smell suddenly.

• Rotten smell in well water suddenly

  Sudden well-water odor often reflects changes in groundwater chemistry, a failing pump, or contamination that warrants testing.

All Articles in This Cluster

• Rotten egg smell in hot water
• Sulfur smell only in cold water
• Odor that worsens when heater runs
• Rotten smell after water heater replacement
• Sulfur smell after city water outage
• Sulfur smell after plumbing repair
• Rotten smell after winterization
• Egg smell after installing filter
• Egg smell after backflow install
• Egg smell after long vacation
• Sulfur odor when running shower
• Smell only in upstairs bathroom
• Smell only in kitchen sink
• Sulfur odor in laundry water
• Odor only in first water draw
• Smell disappears after flushing system
• Smell returns every few weeks
• Rotten smell in well water suddenly