Why does my water smell or have an odor?

We often assume our drinking water is pure H20, but it is not just hydrogen and oxidation.  Water is the universal solvent and can contain a host of natural minerals and ions, natural and man-made chemicals and even microbiological agents.   With respect to drinking water, the EPA drinking water standards are designed and assumed that your drinking water is 99.95 % pure (NOT 100 %).  Thousands of contaminants might be present in your water, and it would normally be much too expensive to test for every possible contaminant. However, there are some simple, inexpensive tests, and visual/ aesthetic clues that can act as “red flags” for possible contamination or a change in your drinking water quality. With respect to changes in the aesthetic quality of the water, our eyes, nose, and mouth are great detectors and indicators of change. In many cases the aesthetic quality of the water is governed by the secondary drinking water standards.

The source of odor can depend on a number of factors, such as:

1.       What is the source of your drinking water?   City water, Groundwater, Rainfall Catchment, or surface water.  

2.     Is your drinking water from a regulated public water system or a private water supply ?  Please remember that most private water systems are not regulated and not regularly monitored by a third-party agency. 

3.      If the water was treated, how was the water treated ?

4.      How are you getting the drinking water and what is the make-up and composition of the distribution system?

The smell of your drinking water or the associated odors are what we at Know Your H20 Level 1 testing or monitoring.  Level 1 Testing is YOU. It is done with simple observations that you can make using your senses of sight, smell, taste, touch, and readily available information about the home. These observations can be observed in the moment or monitored as they change over time. What you see, smell, taste, or problems you are experiencing with your water, your home, or yourself should be noted and recorded. These are basic observations you can make that might help diagnose your water-quality-related problem or condition.   It is also important to keep in mind that sometimes the smell of the water is also related to the water taste and its other aesthetic qualities, so do not forget to think about the visual appearance, taste, or other observable properties.

There is no primary drinking water standard for water odor, but there is a secondary drinking water standard for odor.  The threshold odor number for a regulated water in the USA is a threshold odor number of 3.

More on the Threshold Odor Number and Odor - 

The following are the most common types or classes of odors:

Does it smell like Dirt, Earthy, Grassy, Fishy or Wet Dog ?

Smells that individuals may report as being Dirty, Earthy, Grassy, or Fishy could be related to the presence of bacteria, dissolved organic material,  fungi, mold, low levels of hydrogen sulfide, algal by-products, or actual “Dirt/ Sediment” in the water. In some cases, the odors may be intermittent and/or seasonal.   For example, city water customers that have a drinking water source that is a surface water may have an earthy or musty odor during the summer months because of the presence of geosmin in the water. 

“Geosmin is an irregular sesquiterpenoid (“Sesquiterpenes are a class of terpenes that consist of three isoprene units and often have the molecular formula C₁₅H₂₄”)  with a distinct earthy or musty odor, which most people can easily smell. The geosmin odor detection threshold in humans is very low, ranging from 0.006 to 0.01 micrograms per liter in water. Geosmin, along with the irregular monoterpene 2-methylisoborneol, together account for the majority of biologically-caused taste and odor outbreaks in drinking water worldwide and in farmed fish.” (Source)

If the water has an odor after a period of not using the water, the odor may be related to the presence of a stagnant flow condition in the piping and the regrowth of various biological agents that can include: fungi, mold, bacteria, nuisance bacteria, and even some potential pathogens.     If the water has a fishy smell, the problem may be related to algal by-products, ammonia compounds reacting with chlorine, the presence of barium (fishy smell) or cadmium (fishy and metallic odor).  The wet dog smell make be related to the presence of low levels of volatile organics in the water reacting with bacteria or organics generated by the bacteria themselves.

Contaminant Summary: Dirt, Earthy, Grassy, Fishy or Wet Dog -Fungi, Molds, Bacteria, Standard Plate Count, Dissolved Organic Material, Barium, Cadmium, Algal By-products (Geosmin), Low levels of hydrogen sulfide, petrochemical contamination and possible PCB contamination.

Does it smell like Rotten Eggs?

Water smelling like rotten eggs is not uncommon in the area where I grow up.  Typically, this problem is associated with the presence of hydrogen sulfide gas in the groundwater that is naturally occurring or associated with bacterial contamination by sulfate related bacteria.   In some cases, the cause is not the actual source of the water, but the presence of high levels of sulfate in the water and prolong periods of stagnant flow conditions or biological regrowth within a distribution system.  Occasionally, a hot water heater is a source of hydrogen sulfide odor. The magnesium corrosion control rod present in many hot water heaters can chemically reduce naturally-occurring sulfates to hydrogen sulfide.  In addition to microbiological agents, the odor may be related to the presence of manganese (creates a sulfur like odor), organic material, petrochemical decomposition, and sulfur compounds like mercaptans.

“The odor of water with as little as 0.5 ppm of hydrogen sulfide concentration is detectable by most people. Concentrations less than 1 ppm give the water a "musty" or "swampy" odor. A 1-2 ppm hydrogen sulfide concentration gives water a "rotten egg" odor and makes the water very corrosive to plumbing. Generally, hydrogen sulfide levels are less than 10 ppm, but have been reported as high as 50 to 75 ppm.”

Contaminant Summary:  Sulfur or Rotten Egg Smell - elevated level of Hydrogen Sulfide, manganese, mercaptans (sulfur compounds), organic decomposition, petrochemical-related organics, and Sulfate-Reducing Bacteria.

Oily, Fuel, Chemical or Fruit Smells ?

This type of strong odor is typically associated with a volatile organic compound or semi-volatile organic compound, such as gasoline, fuel oil, kerosene, petrochemical contamination, natural and man-made organic compounds, aldehydes (found in solvents), hydrocarbons, PCBs, and in some cases very significant bacterial growth.   If this occurs, we recommend that you check the back of the toilet tank to see if the water has a metallic sheen.  If you break-up the metallic sheen and the sheen comes back together, it is more likely a hydrocarbon or chemical issue.  If the sheen stays broken appear with square edges it is most likely a bacterial problem and the bacteria is likely one of the nuisance bacteria and/or heterotrophic bacteria.

Note: If the odor has a perfume smell, we recommend adding a surfactant test (Foaming agents). 

Does it smell like Metal ?

This type of problem may be experienced by having water with a metallic smell, but also a metallic, bitter taste.  Look for other warning signs of a problem, like coating, films, precipitates, or staining that is colored.  Metallic taste typically related to high levels of metals, such as: cadmium, chromium, copper, manganese, nickel, lead, and/or even zinc or it can by associated with low pH or acidic water.  The source of the smell could be related to the water source or corrosion within the distribution system.   In some cases, this smell may also be related to the presence of nuisance bacteria.    

Does it smell like chlorine?

This is more commonly a problem with City Water customers that get their drinking water from a community water system or regulated system that uses chlorine to disinfect the water and maintain a disinfection chlorine residual in the water. A common problem that customers report includes the following: "my water smells like a pool", the water "burns my eyes or dries my skin", or "the water tastes like chlorine". The elevated level of chlorine in the water may be an attempt by the utility or authority to manage taste, odor, and aesthetic issues and Bacterial issues within the distribution system or to disinfect a recent repair to the distribution system.

The EPA requires treated tap water to have a detectable level of chlorine to help prevent contamination of the water between the water source and the user. The allowable residual chlorine levels in drinking water (up to 4 parts per million) pose “no known or expected health risk with an adequate margin of safety" and most community water distribution systems have chlorine residuals ranging from 0.2 to 0.5 mg/L. A chlorine residual is maintained in the distribution system to inhibit Bacterial regrowth, prevent the creation of nuisance conditions in the distribution system, and provide a final barrier to prevent Waterborne Disease.

Elevated levels of chlorine or other disinfections may be associated with the presence of disinfection by-products, such as trihalomethanes or haloacetic acids (HAAs).  Some Disinfection By-Products have been identified as Cancer Group 3 carcinogens. These are compounds that have been shown to cause cancer in animals which suggests that there is a high risk of cancer in humans. In addition, health studies and assessments show there is potentially a high risk of kidney, liver, and nervous system damage.

Actions

If you are experiencing odor issues we recommend the following:

1.      Document the problem – make sure to write down the time and date when this started and where it was noticed and always check the toilet tank (Take a Photo).

2.      It is a specific faucet, remove the faucet aeration device and check for debris or foreign material (Take a Photo).

3.      Check to see the odor is on the incoming water to the home, all the water spigots, and in both the hot and cold water.   Make sure to cover the sink or basin drains when running the water, to avoid detecting odors from the sanitary drain.

4.      The solution depends on what you find and your situation.  In some cases, you may be able to flush the water line, contact the water supplier, shock disinfect the system, or install a long-term treatment approach, but before you install treatment, we recommend some Level  2 screening and/or Level 3 testing.

Level 2 Screening

Well Water or City Water - Safe Home® 14-in-1 Drinking Water Test Kit

Home Check – Airborne Mold Check

Home Check – Indoor Air Quality (VOCs)

Level 3 Screening

Well Water

Problem Check (Musty Odor/ Sulfur)   for Sulfur odors make sure to add a Sulfate Related Bacteria Test.

Corrosion Check (Metallic Odor)

Well Test Deluxe (Petrochemical or SOC Concerns and Fruity Odor)

City Water  and add a Total Coliform Bacteria Test as an add on 

If your city water has a possible problem with sulfur – rather than adding the Total Coliform add on – You will need the Suspected bacterial problem (Sulfur) – Add on.

If your city water has a possible problem with iron and manganese  – rather than adding the Total Coliform add on – You will need the Suspected bacterial problem (Iron) – Add on.

Summary of Article by Grok 3 (7/30/2025)
"The article from Know Your H2O discusses common drinking water odors, their causes, and solutions:

1. Rotten Egg/Sulfur Smell: Caused by hydrogen sulfide gas from sulfur bacteria in water heaters, wells, or plumbing. While low levels are generally safe, high levels can cause nausea or corrosion. Solutions include replacing the water heater’s magnesium anode, shock chlorination, or installing filtration systems.
2. Musty/Earthy Smell: Often due to iron bacteria, mold, fungi, or algal blooms in water sources. Reverse osmosis or activated carbon filtration can reduce this odor.
3. Metallic Smell: Results from deteriorating metal pipes (e.g., iron, manganese, zinc, or copper). While traces are typically harmless, lead in older homes (pre-1986) is a concern. Filtration systems can address this.
4. Fishy Smell: Caused by organic matter, bacteria, or chloramine (a disinfectant). Contact your water provider or install a filtration system to resolve.
5. Chlorine/Bleach Smell: Due to excess chlorine used in water treatment, typically safe at 0.2–2.0 ppm. Running faucets or using filtration can eliminate the odor.
6. Sewage Smell: Often from bacteria in drains or stagnant water in heaters. Cleaning drains with baking soda and vinegar or flushing the water heater can help.

The article emphasizes identifying the odor’s source (e.g., drain, heater, or water supply) and recommends professional water testing, filtration systems (like reverse osmosis or activated carbon), or contacting water authorities for persistent issues."