Rotten Eggs Smell in Well Water: Causes, Testing & Treatments

It is not unusual to find that the well water running from the tap has a foul smell or tastes bad. Minerals or other substances can easily latch onto the water and impart their properties. It is important to know that all minerals present in water are not harmful. Some are even required by the human body, such as iron and some useful bacteria. However, the stench in drinking water can make it unappealing. One typical smell that can be found in well water is rotten egg smell.

According to the Center for Disease Control and Prevention (CDC), around 15 million households use private wells to meet their water needs. Wells extract the water that can be found underground. Groundwater can be exposed to all sorts of substances present in the soil. Consequently, it can dissolve several useful as well as harmful chemicals. If you own a private well, you may have encountered this problem before. If not, it is good to know beforehand how to prevent well water from smelling like rotten eggs.   

Causes of Rotten Egg Smell in Wells

The rotten egg smell in the water is mostly caused by hydrogen sulfide gas (H2S). Hydrogen sulfide gas can occur naturally in the earth as a result of soil and rock decomposition. As the gas evaporates rapidly, it is mostly found in groundwater than in surface water.

Another reason for the smell can be when sulfates in the water convert to form hydrogen sulfide. The gas-emitting sulfur bacteria present in the water utilize oxygen in the sulfate to produce the gas. If you notice a slimy substance impeding the water flow, it can indicate that sulfur bacteria have nurtured in the water. Sometimes, the sewage discharge can also cause rotten egg odor in the water.

Common Indicators

Some signals, besides the rotten egg smell, indicate the presence of sulfur bacteria in the water:

  • Black, rusty, white or grey slime in water
  • Corroding pipes: metal chips have mixed in with the water
  • Black stains visible on kitchenware, bathtubs and plumbing fixtures
  • Beverages and food discoloration

 Harmful Effects

Hydrogen sulfide gas generally does not pose a threat to health. However, elevated levels can cause diarrhea, nausea, or dehydration. If the rotten egg smell is caused by sewage or other dangerous contaminant mixed with the water, it can have adverse effects on health. According to research,

Levels of sulfates above 250 ppm (or mg/L) can cause dehydration and have a laxative effect. Notably, children are more prone to its side-effects.

Find the Source of Hydrogen Sulfide Gas

It is essential to know the exact source of the smell before you focus on implementing a solution. If the odor is only in hot water, there might be a problem with the water heater. The magnesium rod in the water heater can produce hydrogen sulfide gas after reacting with the sulfates. Replacing the magnesium rod with aluminum or zinc rod can help resolve the issue. Other times, increasing the temperature of the water heater or disinfecting with a chlorine bleach solution can do the trick. Make sure not to injure the skin while dealing with the hot water. It is advisable to contact a professional plumber or boiler inspector to fix the problem.

If the cold water also smells like rotten eggs, the water softener may be the source of the problem. A water softener can become a favorable environment for the sulfur bacteria to grow and produce hydrogen sulfide gas. It is essential to clean the tank once every year to prevent the growth of gas-emitting bacteria.

If there is no problem with the water heater or water softener, try running the faucet for a few minutes. If the smell goes away, there is likely an issue with the well water or plumbing system. If the smell persists, there is a high probability that hydrogen sulfide gas is present in your groundwater.  

Hydrogen Sulfide Level Testing Methods

Private well owners must get their well water checked every year for any contaminants. Sulfide levels in the water up to 0.35 mg/L are barely noticeable. Levels above 0.4 mg/L can taste rather unpleasant in drinking water.

To check for hydrogen sulfide gas in the water, one or more of the following methods can be used:

Observation Method

The distinctly foul rotten smell of hydrogen sulfide gas can be detected quite easily. You might want to check if the odor is caused by sewage waste mixing with the water. If it is sewage pollution, it is crucial to get the water tested for coliform bacteria.   

Water Testing Kits

Test water at home

Home-based water testing kits are also available to check the hydrogen sulfide level in the water. These kits consist of paper strips, chart, and instructions. Carefully follow the instructions to get reliable results. If there is no indication of the gas, the smell could be because of sewage waste mixed with the water. In this case, you may have to seek professional help.  

Expert Opinion

If you suspect well water contamination, you can seek help from the local health community or sending a sample of the water to well water system experts. They can assist in analyzing the water quality or advise you on relocating the well if need be.

Useful Tips

  • The location of the well is critical. There must be an appropriate distance between the well and any agriculture, industrial discharge areas, or landfill.
  • After a natural disaster such as floods or heavy rainfalls, check the well water for any contaminants. You can also contact the local health community or licensed well water contractors to guide you.
  • Avoid using or disposing fertilizer, agriculture, pharmaceutical, or pesticide waste near normal, dry, or abandoned wells.
  • Contact a licensed well driller for building, adjustment, or closing of a well.

 How to Get Rid of Rotten Egg Smell from Well Water

Environmental Protection Agency (EPA) regulates public water systems. However, the Authority does not monitor private wells but does guide how you can remove contaminants from the well water.

Several procedures are available to remove the rotten egg smell in the water. Depending on the simplicity of the process, cost of installation, and maintenance, you can select the method most suitable to your needs:


Ozone Treatment: Ozone can be used to treat the sulfur in the water. This method is effective in removing levels up to 10 ppm.  

Activated Carbon Filter: These filters can be effective in removing levels as much as 0.3 ppm. However, the carbon filters can wear out quickly, and this method may not be very effective for eliminating levels above 0.3 ppm.  

Reverse Osmosis: Reverse Osmosis is an effective method to rid the water of several contaminants like iron, lead, copper, manganese, etc. It can also be used to remove large concentrations of hydrogen sulfide from the water. If the water contains concentrations as large as 250 ppm, then reverse osmosis is your best choice. 

Iron Removal Filter Method: This filtration system can rid the water of hydrogen sulfide, iron, and manganese. The filter can reduce the water of hydrogen sulfide to an amount of 10mg/L. It oxidizes the hydrogen sulfide to make it easily removable. The residual insoluble sulfates can be filtered out to obtain odor-free water. However, you may have to keep an eye on the filter for any residual sulfates, which can hinder the filtering process.  

Chlorination: An automatic chlorination filter is another method to remove hydrogen sulfide gas from the water. The chemical can remove levels over 6mg/L. Chlorine bleach can remove iron and manganese from the water as well. However, to avoid the chlorine taste in water, a de-chlorinating carbon filter may have to be used. It can also rid the water of any sulfur content.  

Water purification via aeration

Aeration: This process involves passing air at high pressure through the water. As a result, the harmful molecules are separated, leaving behind contaminant-free water. Aeration does not eliminate the hydrogen sulfide from the water but removes its contaminants to a bearable level. It can remove levels lower than 2.0 ppm. If you use aeration, you might have to vent the system and clean the storage tank occasionally. Otherwise, the smell can accumulate near the aerator, and algae can build up over time. 

Read more: 9 Reason Why Water Stinks & Perfect solutions to Fix it


Well water must be checked for any contamination at least once a year. If the water becomes contaminated, there is also the option to relocate the well. However, it can be much more complicated than using a home-based water filtration system. The relocated well is not guaranteed to be safe from other contaminants in the water. The water source could already be tainted with sulfides or other harmful substances. Therefore, a more reliable investment can be to install a water filtration system.


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