Why Does My Well Water Suddenly Smell Like Rotten Eggs?

You turn on the faucet and—ugh—your water smells like rotten eggs. If this started suddenly, you're probably alarmed and wondering what's wrong with your well. The good news: in most cases, this smell isn't dangerous and can be fixed. The sulfur odor comes from hydrogen sulfide gas, and understanding its source is the key to eliminating it.

What Causes the Rotten Egg Smell?

The distinctive rotten egg odor in well water is hydrogen sulfide (H₂S) gas. Several sources can introduce this gas into your water:

1. Sulfur-Reducing Bacteria in the Well

Most common cause. Naturally occurring bacteria thrive in groundwater and feed on sulfates in the soil. As they consume these sulfates, they produce hydrogen sulfide as a byproduct. These bacteria often colonize wells, especially in stagnant areas of the casing.

Signs this is your problem:

• Smell is present in both hot and cold water
• Smell is strongest first thing in the morning or after water sits unused
• You may see a slimy coating on fixtures or inside the toilet tank

2. Water Heater Anode Rod Reaction

Very common—and often overlooked. Your water heater contains a magnesium anode rod designed to prevent tank corrosion. When this magnesium reacts with sulfates naturally present in well water, it creates hydrogen sulfide gas.

Signs this is your problem:

• Only hot water smells like sulfur
• Cold water smells fine
• Problem started after getting a new water heater or letting it sit unused

3. Changes in the Aquifer

Groundwater chemistry isn't static. Drought, heavy rains, nearby construction, or changes in water table levels can alter the mineral and bacterial content of your water source.

Signs this is your problem:

• Smell appeared suddenly without any changes to your system
• Neighbors with wells report similar issues
• Recent weather events (drought ending, heavy rains)

4. Contamination or Decay

Less common but important to rule out. Organic matter in the well (dead insects, animals, or plant material) can decompose and create hydrogen sulfide.

Signs this may be your problem:

• Very strong, persistent smell
• Well cap is damaged or missing
• Water also looks cloudy or has particles

Is Sulfur Smell in Well Water Dangerous?

At the concentrations typically found in residential wells, hydrogen sulfide is more unpleasant than dangerous. However:

• Low concentrations (0.5-1 ppm): Noticeable rotten egg smell. Generally safe but unpalatable.
• Moderate concentrations (1-5 ppm): Stronger smell. Can cause mild nausea for sensitive individuals. Can tarnish silverware and copper fixtures.
• High concentrations (5+ ppm): Very strong smell. Should be treated. Can corrode plumbing over time.
• Very high concentrations (50+ ppm): Rare in wells. Genuine health concern. Immediate treatment needed.

Important: While the smell itself may not be dangerous, it can indicate bacterial contamination. We recommend professional water testing to check for both hydrogen sulfide levels and bacteria.

How to Fix Sulfur Smell in Well Water

The right solution depends on the source of the problem:

Solution 1: Shock Chlorination (For Bacteria)

If sulfur-reducing bacteria are the cause, shock chlorination often solves the problem. This involves adding a concentrated chlorine solution to the well to kill bacteria.

Caution: Improper chlorination can damage your well or pump. If unsure, have a professional do it. Learn more about well shock chlorination.

Solution 2: Replace Water Heater Anode (For Hot Water Only)

If only your hot water smells, replace the magnesium anode rod with:

• Aluminum/zinc anode: Doesn't react with sulfates. Most common solution.
• Powered anode: Uses electrical current instead of sacrificial metal. More expensive but eliminates the problem permanently.

Cost: $50-$100 for the anode, $150-$300 installed by a plumber.

Solution 3: Aeration System (For Persistent Issues)

Aeration introduces air into the water, which oxidizes hydrogen sulfide and releases it as a gas before it reaches your fixtures.

• Very effective for moderate to high H₂S levels
• No chemicals needed
• Also helps remove iron and manganese
• Cost: $1,500-$3,500 installed

Solution 4: Activated Carbon Filter

Carbon filters adsorb hydrogen sulfide as water passes through. Best for low to moderate levels.

• Simple installation and maintenance
• Also improves taste and removes chlorine
• Requires periodic filter replacement
• Cost: $800-$2,000 installed

Solution 5: Oxidizing Filter (Iron/Manganese Filter)

These filters use manganese dioxide or other media to oxidize and remove hydrogen sulfide along with iron and manganese.

• Effective for higher H₂S levels
• Also addresses iron staining
• Requires periodic backwashing
• Cost: $1,200-$3,000 installed

Solution 6: Chemical Injection System

For severe cases, a chlorine or hydrogen peroxide injection system continuously treats water before it enters your home.

• Most effective for very high H₂S levels
• Also provides continuous disinfection
• Requires chemical replenishment
• Cost: $1,500-$4,000 installed, plus ongoing chemical costs

Treatment Comparison Chart

When to Call a Professional

Contact a well water professional if:

• The smell is very strong or getting worse
• Shock chlorination didn't solve the problem
• You're unsure of the source
• Water has other quality issues (color, sediment, other odors)
• You want to install a permanent treatment system
• You're buying or selling a home with this issue

Preventing Future Sulfur Smell

Once you've solved the problem, these practices help prevent recurrence:

• Annual well inspection: Catch bacterial issues early
• Maintain your well cap seal: Prevents contamination entry
• Periodic chlorination: Consider annual maintenance chlorination
• Water heater maintenance: Check anode rod condition every few years
• Don't let water sit: Run taps periodically if a home sits vacant

Frequently Asked Questions