Sulfur / Rotten Egg Smell in Hot Water

The "rotten egg" smell from hot water is hydrogen sulfide (H₂S) gas — produced when sulfate-reducing bacteria in well water react with the magnesium anode rod inside the water heater. Cold water typically has no smell because the bacteria don\'t produce H₂S in cold water.

Why it happens

1. Sulfate-reducing bacteria are present in some well water sources
2. Bacteria thrive in the warm, low-oxygen environment inside the water heater tank
3. Bacteria react with the magnesium anode rod, reducing sulfate to sulfide
4. Sulfide combines with hydrogen to form H₂S gas — the rotten egg smell

Step 1: Confirm hot-only smell

• Smell in hot only, cold clear: water heater issue. Continue below
• Smell in both hot and cold: supply-side bacterial contamination. Treat the whole well system

Solution 1: Switch anode rod (most common fix)

• Replace magnesium anode with aluminum-zinc anode. Eliminates the sulfide reaction
• $25-40 part, 45-minute DIY
• Camco and universal anode rods available in aluminum-zinc
• Don\'t switch to no anode — tank corrosion will follow

Solution 2: Powered titanium anode (premium fix)

• Uses electrical impressed current instead of sacrificial metal
• No reaction with sulfate bacteria — eliminates smell permanently
• $120-200 part; 20+ year lifespan
• Requires 120V outlet near water heater

Solution 3: Shock-chlorinate the tank

One-time treatment to kill the bacteria currently in the tank:

1. Drain tank
2. Add 1-2 cups household bleach to the tank via the anode port
3. Refill tank fully; let sit 2-3 hours
4. Drain again; refill with fresh water
5. Run hot taps until bleach smell clears

Pairs with anode swap for best results.

Solution 4: Step up to Marathon or stainless

Marathon composite tank or Westinghouse stainless tank don\'t use anode rods. No sulfide reaction possible. Premium fix for chronic problem households on well water.

What doesn\'t work

• Just flushing the tank — bacteria recolonize within weeks
• Lowering temperature — H₂S production continues
• Removing the anode rod — accelerates tank corrosion
• Adding chlorine to the well — small effect; bacteria in tank persist

Bottom line

Switch magnesium anode to aluminum-zinc, then shock-chlorinate the tank. Most common fix for well-water rotten egg smell. For chronic recurrence, powered titanium anode or Marathon composite tank are permanent solutions.