Rotten egg smell from water or hot water taps

Common Causes

1. Hydrogen sulphide (H2S) gas dissolved in groundwater from sulfate-reducing bacteria
2. Magnesium anode rod in water heater reacting with softened water (hot water only)
3. Sulphur-reducing bacteria growing in a stagnant well or distribution system

What You Can Try First

1. If smell is only from hot water: the magnesium anode rod in your water heater may be reacting with softened water to produce hydrogen sulphide. Consider replacing with an aluminum/zinc anode rod (consult a plumber first — removing the anode rod voids many warranties).
2. Run cold water from the tap for 30 seconds — if cold water also smells, the source is the well, not the water heater.

When to Call a Pro

• Rotten egg smell is present from cold water taps (sulphide in the well — requires treatment system)
• Cold water smells of sulphur — requires water testing and a treatment system
• Hot water smell persists after running the heater on a "sanitize" cycle
• Smell has recently appeared or worsened — may indicate well contamination
• Smell is strong and pervasive throughout the home

Alberta Context

Hydrogen sulphide in well water is a known issue in parts of Red Deer County and Mountain View County, particularly in deeper aquifers. Even at concentrations below Health Canada's 0.05 mg/L guideline, the odour is detectable and objectionable. Treatment options include aeration, chlorination, or catalytic carbon filtration depending on concentration. Always test the well water before investing in treatment equipment.