Why Does My Tap Water Smell Like Rotten Eggs? Causes & Fixes

That "rotten egg" or sulfur smell is one of the most common water complaints, and the good news is it's almost always hydrogen sulfide gas — not a sign of sewage contamination. Here's how to figure out where it's coming from and what actually fixes it.

Step 1: Isolate Where the Smell Comes From

Run this quick test to narrow down the cause:

• Only hot water smells → almost always the water heater's anode rod reacting with sulfate bacteria in the tank
• Both hot and cold smell, only at one faucet → likely a drain trap or garbage disposal issue, not the water itself
• Both hot and cold smell at every faucet → the water source itself (well or, rarely, municipal supply) contains hydrogen sulfide or sulfate-reducing bacteria

Common Cause 1: The Water Heater Anode Rod

Most tank water heaters use a sacrificial magnesium or aluminum anode rod to prevent corrosion. That rod can react with naturally occurring sulfate-reducing bacteria inside the tank, producing hydrogen sulfide gas — the classic sulfur smell. This is extremely common in homes on well water, and can also happen on municipal water in the right conditions.

Common Cause 2: Well Water and Groundwater Chemistry

If cold water smells at every tap, the hydrogen sulfide is likely coming from the aquifer itself, or from bacteria colonizing the well casing, pressure tank, or pump. This is common in areas with naturally sulfate-rich or organic-rich groundwater. Private well owners should treat any new or worsening odor as a signal to test — see our private well testing guide for what to check and how often.

Common Cause 3: Municipal Water (Less Common)

Public water systems occasionally have sulfur odor issues tied to source water changes, low chlorine residual in distant parts of the distribution system, or stagnant water in low-use pipes. If you're on a public system, check your utility's Consumer Confidence Report and compare your system's record on WaterQ's search.

When to Be Concerned

1. Sudden onset after flooding or nearby construction — get a bacteriological (coliform/E. coli) test
2. Smell plus discoloration or cloudiness — stop drinking until tested; see our guide to discolored water
3. Private well with no prior odor history — test annually regardless, and immediately if the smell is new

Filtration Options for Sulfur Odor

For whole-house sulfur odor that isn't resolved by fixing the water heater, treatment options include aeration systems, oxidizing media filters (often using potassium permanganate-regenerated manganese greensand), and catalytic carbon filters rated specifically for hydrogen sulfide — a standard carbon or sediment filter usually isn't enough on its own.