Rotten egg smell in well water

A rotten egg smell in drinking water is most commonly caused by hydrogen sulfide gas (H₂S). This gas occurs naturally and can give water a strong sulphur or rotten egg odour. The smell is more noticeable when water is heated or left standing.

Hydrogen sulfide in drinking water may come from natural or system-related sources, including:

• natural breakdown of organic matter in groundwater
• sulphur-reducing bacteria present in wells or plumbing
• interaction between sulphate in water and bacteria
• water heaters, especially those with magnesium anode rods

The smell may originate in the well, plumbing system or hot water system.

Hydrogen sulfide does not have a health-based Maximum Acceptable Concentration. At typical levels found in drinking water, it is considered an aesthetic issue rather than a health concern.

Hydrogen sulfide has an Aesthetic Objective of 0.05 milligrams per litre (mg/L), based on taste and odour.

Laboratory testing can help confirm the presence of hydrogen sulfide or sulphate in drinking water and identify related water quality issues.

Testing recommendations include:

• use of an accredited laboratory
• collection of samples following laboratory instructions

For more information on water testing services, please see: Well water testing. Testing costs vary depending on the laboratory and the number of parameters analyzed.

Hydrogen sulfide in drinking water is not usually a health concern at levels that cause taste or odour problems. However, high concentrations may cause:

• unpleasant taste and smell
• nausea in some individuals

Health risks from hydrogen sulfide in drinking water occur primarily through ingestion. Water with a strong sulphur smell may still be used for:

• bathing
• handwashing
• dishwashing

When a rotten egg smell is present, identifying the source is important. Odour may originate from the well, plumbing or hot water system. Actions that may help reduce odour include:

• inspecting and maintaining the well
• flushing plumbing systems
• servicing or adjusting the water heater
• confirming whether the odour occurs in hot water, cold water or both

Boiling water does not remove hydrogen sulfide and may increase odour. Treatment systems may be installed at the point where water enters the home or directly at a tap. Effective treatment options include:

• aeration systems
• activated carbon filtration
• oxidation followed by filtration
• chlorination or other continuous disinfection methods

Treatment systems should be certified to meet current NSF standards and installed and maintained according to the manufacturer’s instructions. More frequent testing is recommended to confirm treatment performance.

Additional information on treatment options is available through private water treatment companies or the nearest regional Health Protection Branch office.