The incidence of "rotten egg" sulfur odors and resulting black water in hot and cold water lines is due to the reaction of sulfates and microorganisms. This may occur in the well, in household plumbing, or specifically in the water heater and hot water lines.
Hydrogen Sulfide and Sulfur Bacteria in Well Water
Hydrogen sulfide gas (H2S) gives water a characteristic "rotten egg" smell. It may occur naturally in groundwater or be produced by sulfur bacteria. Understanding the source helps determine the appropriate treatment method.
Sources of Hydrogen Sulfide
Hydrogen sulfide may come from:
- Natural groundwater chemistry
- Sulfur bacteria in the well, distribution system, or water heater
- Pollution (rare)
Are Sulfur Bacteria or H2S Harmful?
Sulfur bacteria are not harmful, but H2S in high concentrations can be dangerous. It’s important to vent enclosed areas like well pits or basements. Always test your water for coliform bacteria and nitrates to rule out contamination.
Other Issues
Sulfur bacteria produce slime and may promote other bacterial growth, such as iron bacteria. This slime can clog plumbing. H2S may also stain plumbing fixtures and corrode metal pipes.
What Causes It?
Organic decay or sulfate minerals in soil/rock can create H2S. Sulfate-reducing bacteria transform dissolved sulfate into gas as water moves underground.
How to Diagnose the Source
Smell the water from various taps. The odor is strongest in hot water due to gas vaporization. Check after being away from home, when your nose is more sensitive. Lab testing for H2S, sulfur bacteria, and iron bacteria is recommended.
If the Smell Is Only in Hot Water
The water heater is likely the issue. Try these steps:
- Disinfect the heater with bleach (1 cup per 5 gallons).
- Temporarily raise water temp to 160°F to kill bacteria.
- Replace or remove the magnesium anode rod. Consider a zinc/alumi