Why Does My Well Water Smell Like Rotten Eggs?

The Rotten Egg Smell: Hydrogen Sulfide

That unmistakable rotten egg odor in your well water is hydrogen sulfide gas (H₂S). It's one of the most common water quality complaints we hear. While usually not dangerous at low levels, it makes water unpleasant to use and can indicate other problems.

What Causes It?

1. Sulfur-Reducing Bacteria

The most common cause. These bacteria live in oxygen-poor environments (like wells) and convert sulfates in groundwater to hydrogen sulfide. They're not harmful to humans but produce that horrible smell.

2. Naturally Occurring Sulfur

Some aquifers contain naturally high sulfur levels from geological formations. This is common in certain areas of Southern California.

3. Water Heater Issues

If the smell is only in hot water, your water heater's magnesium anode rod may be reacting with sulfates. This is an easy fix.

4. Well Contamination

In some cases, organic matter or surface contamination can introduce sulfur bacteria.

Solutions That Work

For Bacteria-Caused Odor:

• Shock chlorination — Kill bacteria throughout the system
• Continuous chlorination — Chlorine injection system
• Aeration — Introduce oxygen to kill bacteria

For Naturally Occurring Sulfur:

• Oxidation filtration — Greensand or Birm filters
• Aeration systems — Release gas before it enters home
• Carbon filtration — For lower levels

For Water Heater Issues:

• Replace anode rod — Switch to aluminum or zinc
• Increase temperature — Temporarily to kill bacteria

Testing Your Water

Before choosing a treatment, test your water to identify:

• Hydrogen sulfide level (ppm)
• Sulfate level
• Bacteria presence
• Iron and manganese (often co-occur)