Tips for Taps Blog

Guide to Well Water Contamination

How To Spot Well Water Contamination


Not all water pollutants are easily detectable, but knowing how to read certain signs can help you test and treat a few common water quality issues.

Even seemingly harmless changes to water quality usually means something is getting into your well water that wasn’t there before. Your water's appearance, smell, and taste are often important clues to finding these potential hazards. We’ll go over sense-based signs—like cloudiness, gunk, or weird smells—that can help guide you to the source of the problem. 

Table of Contents:

Why Is My Well Water Orange or Reddish Brown?

Iron, iron bacteria, tannins and manganese can cause your water to become orange, red, or brown.  

Likely Sources

Iron and manganese are naturally occurring and commonly found together in groundwater. Nearby mining can cause elevated levels of these metals in local water supplies. Iron can also enter your well water from corrosion in well casings and pipes. 

Iron bacteria naturally occur in groundwater and grow by feeding on iron. This can cause a build up of red or brown slime called a “biofilm” and change the color of your water. 

Tannins are the organic debris from dirt, plant matter and other natural material that reaches well water after leaves and organic matter decompose. 

Health Risks

      • Iron and iron bacteria are not necessarily harmful to health, but they can indicate or lead to other hazards
      • The biofilm produced by iron bacteria creates ideal conditions for more harmful organisms to grow. This slime can also affect your well flow, corrode pipes, and cause clogging.
    • Manganese is generally considered non-toxic, though some studies have linked long term exposure to high concentrations with negative health effects on the nervous system.
    • Signs of corrosion can also signal a health risk if your plumbing contains lead, which cannot be detected by smell, taste, or appearance. 

See our guide on discolored water for treatment options.

Why Is My Well Water Yellow?

Iron, iron bacteria, tannins and manganese can also cause water to turn yellow

Likely Sources

If the yellow water is totally transparent and the color does not settle out with time, this means iron and manganese have combined with organic matter (called tannins) to form colloidal or organic iron.

Colloidal iron is more commonly found in surface water than in groundwater, which could be a sign that your well is being contaminated by runoff. 

Health Risks

Why Is My Well Water Blue?

Copper is the most common culprit for turning water blue and leaving blue-green stains on fixtures. 

Aluminum is another potential cause of blue-tinted water at very high concentrations. 

Likely Sources

Copper in your water supply is most likely caused by corrosive water dissolving the metal in your plumbing. However, low amounts of copper can be naturally found in surface and groundwater sources. Mining, farming, manufacturing operations, and industrial wastewater also may cause elevated copper levels. 

Aluminum occurs naturally but can enter groundwater through leaching from coal-fired power plants and incinerators.

Health Risks

      • At low levels, copper in drinking water is not thought to cause health symptoms.
      • At high levels, copper can cause digestive distress—like nausea, vomiting, diarrhea and stomach cramps—especially for children. Copper has also been associated with liver and kidney disease.
      • Aluminum may be associated with neurological disorders like Parkinson’s disease, Lou Gehrig’s disease (ALS), and Alzheimer’s disease. Evidence is largely undetermined as it relates to drinking water. 
    • Signs of corrosion can also signal a health risk if your plumbing contains lead, which cannot be detected by changes in your water’s smell, taste, or appearance.

See our guide on aluminum and our upcoming guide on copper for treatment options.

What Causes Brown or Black Gunk on Fixtures?

Iron and manganese are usually the cause behind black and brown sludge found on fixtures.

Likely Sources

When iron and manganese react with naturally occurring tannins, they produce black residues

Health Risks 

  • See the health risk section on Orange and Reddish Brown Water for additional information on the risks of iron and manganese.

See our guide on black gunk for treatment options.

What Causes White Residue on Fixtures?

Hard water—caused by mineral deposits of calcium or magnesium—leaves white, chalky spots and scaling. 

Silica minerals can also be responsible for white residues and are often mistaken for water hardness.

Likely Sources

Water with very high hardness and related mineral content is typically sourced from limestone aquifers.

Health Risks

    • Hard water doesn’t generally cause any health risks, but scaling can damage your pipes, heating elements, and home appliances (like dishwashers and washing machines).
    • For the latest research on correlations between water hardness and health, read more here.

See our guide on white residue and for treatment options.

What Makes Well Water Cloudy?

Cloudy water can be a sign of many types of contamination including sediment, microorganisms, sewage runoff, dissolved methane gas, or dissolved air (most commonly).

Likely Sources

Sediment—or particles that can range from sand, minerals, plant matter, and microbes—is a common cause of cloudy water. Major disturbances near your well’s water source like drilling, construction, wildfires, or storms can release sediment into the groundwater. 

Dissolved methane gas in your well water can cause cloudiness as it releases into bubbles when drawn from a tap. Methane may naturally occur in well water or can be caused by nearby gas well drilling and landfills. 

Dissolved air will often form tiny bubbles as pressure and temperature force air out of the water and into a gas state. This is common during times of the year when there are changes in pressure and temperature in the atmosphere or changes to your plumbing or distribution system. These air bubbles will often go away very quickly when you watch them in a clear glass

Health Risks

      • Sediment alone may not be a health risk, but it is an indicator of a potential problemthat requires additional testing.
    • The health risks related to sediment are from other pollutants and pathogens that can attach themselves to these particles and enter your water supply. This includes microbes; chemicals like fertilizers and pesticides; and dissolved metals like mercury, lead, and arsenic.
    • Sediment can also damage plumbing, pumps, and water appliances or cause clogs in your water system.
    • Methane gas alone does not cause health problems in drinking water, but is an explosive hazard in poorly ventilated or enclosed areas. 

See our guide on cloudy water for treatment options.

What Causes Oily Well Water?

Iron bacteria are the likely cause behind an oily film or sheen on your water.

Gasoline, petroleum or other oil-based leaks are also common sources of oil sheen on well water. 

Likely Sources

To help narrow down the cause, try stirring a glass of the oily tap water: 

Health Risks

    • Petroleum contamination can cause a range of health hazards—from nerve damage to cancer—depending on the chemicals present in the water.
    • See the health risks section on Orange and Reddish water for additional information on iron bacteria.

What Causes Stinky Well Water?

There are many, many smells and tastes that impact our drinking water experience. Here are some of the most common issues we encounter and the most common culprits and solutions:

Rotten egg smell is usually caused by hydrogen sulfide gas and/or related sulfur bacteria. This gas is normally harmless, but can reach dangerously high levels in enclosed and unventilated spaces. Hydrogen sulfide is also corrosive to iron, steel, copper and brass and may dissolve metals in the plumbing into your drinking water. 

Fishy odors can be caused by algae, bacteria, or the presence of barium or cadmium.

  • Barium occurs naturally and can seep into groundwater near oil drilling, gas wells, and fracking sites. High concentrations can cause blood pressure, muscle weakness, or kidney, liver, and heart damage.
  • Cadmium leaches into pipes through industrial waste. High concentrations can cause kidney, liver, and bone damage.

Moldy and earthy smells are likely caused by algae, fungi, or bacteria growing in your water supply—particularly during warm weather. Tannins can also produce a moldy, or earthy taste and smell (and will often impart a light yellow color to the water as well).

A turpentine odor may indicate there is methyl tert-butyl ether (MTBE) in your water. This comes from leaking underground gasoline storage tanks. MTBE has been shown to cause skin and eye irritation, and some animal studies suggest it is potentially cancer-causing.

Chemical smells in water are often caused by the presence of volatile organic compounds (VOCs). VOCs are a wide group of chemicals that are commonly used in solvents, fuels, paints, and degreasers. Depending on the chemical, VOCs present a range of health risks, including cancer.

See our guide on stinky water for a more complete analysis of smells and related water treatment options.

What Causes Well Water to Taste Weird?

Moldy tasting water frequently comes from iron bacteria. See the sections on Orange and Reddish water for additional information.

Salty water can potentially be caused by chloride or sulfates.

  • Chloride occurs naturally but can reach elevated levels from road de-icing, sewage, industrial waste, and gas well drilling. Chloride itself is not toxic to humans, but may be a sign of sewage or industrial waste entering your water supply.
  • Sulfates occur naturally in groundwater as well. High levels can cause diarrhea and dehydration, especially for infants or individuals not used to drinking sulfates.

Bitter water is also associated with sulfates.

Metallic tasting water usually indicates there are dissolved metals in your water—which can range from iron, manganese, zinc, and copper. This may mean something in your plumbing system is corroding. Depending on the metal, corrosion can be hazardous itself or create conditions for bacterial health risks to grow.

Chemical tastes in water can be caused by the presence of potentially carcinogenic VOCs or pesticides.

See our drinking water taste guide for treatment options.

Why Clear Well Water Isn’t Always Safe

Even if your well water smells, tastes, and appears normal, that doesn’t necessarily mean it’s safe. 

Many pollutants are totally undetectable by our senses—including some of the most hazardous to our health. Lead, E. coli, and arsenic are just a few of the invisible contaminants that can lurk in clear water. Testing your well is likely the only way to ensure you know exactly what's in your drinking water. 

Not sure when to test? Or generally uncertain about well testing?  Private Well Class runs a Pledge to Test Campaign during Ground Water Awareness Week (March 10-16) each year. Private Well Class is a program aimed at boosting the knowledge and competency of individual well owners.

Well Water Tests

Why Trust Tap Score?

We know how confusing it can be to find advice on water quality and treatment you can trust. That’s part of the reason we made Tap Score—to help improve the way you test and treat your drinking water.

  • No affiliate links: Unlike most sites revolving around water quality, we do not take a cut from sales on filtration systems.
  • Unbiased advice: Our blog is independently researched by our team of water scientists and designed to provide clarity on water quality, not to sell treatment products.
  • Independent laboratory testing: Tap Score test results come from SimpleLab's third-party network of certified laboratories; in other words, accredited labs provide the data without conflicts of interest.
  • Continuously updated: Science never rests. That’s why our content always reflects the latest developments in scientific research and regulatory standards.
  • Always available: Our customer service team is the best in the industry and available anytime via chat to answer all your water quality questions.


Article Sources

Stinky Water: Your Odor Guide | SimpleLab

The Drinking Water Taste Guide | SimpleLab Tap Score

The Complete Guide to Discolored Water | SimpleLab Tap Score

Iron and Manganese in Private Water Systems

Iron Bacteria in Well Water - EH

Manganese in Drinking-water

Iron & Manganese in Drinking Water.doc Page 1 of 8 Iron and Manganese (and their removal) in Drinking Water1 Fe/Mn occur nat

Should You Filter Drinking Water For Aluminum? | SimpleLab Tap Score

CAFE: Copper in Private Drinking Water Wells | UMass Center for Agriculture, Food and the Environment

Copper and Drinking Water from Private Wells | Wells | Private Water Systems | Drinking Water | Healthy Water

Copper in Drinking Water: Using Symptoms of Exposure to Define Safety

Aluminum Levels in Brain, Serum, and Cerebrospinal Fluid Are Higher in Alzheimer's Disease Cases Than in Controls: A Series of Meta-Analyses

What's the Black Gunk on My Fixtures?! | SimpleLab

Potential Health Impacts of Hard Water

What's the White Residue on My Fixtures? | SimpleLab Tap Score

What Do Wildfires Mean for My Water Quality?

Hydraulic Fracturing: What It Means for Your Private Well

Sediment & Well Water

Microorganisms: The Good, The Bad, and the Ugly | SimpleLab Tap Score

Methane in Well Water - EH

Residential Environmental and Water Testing FAQs

Public Health Statement for Total Petroleum Hydrocarbons (TPH)

Hydrogen Sulfide in Household Water

8 signs your tap water might be dangerous to drink

Methyl tert-Butyl Ether (MTBE) Factsheet | National Biomonitoring Program

Chloride in Drinking-water

Sulfate in Well Water - EH

How Dangerous Are Pesticides in Water? | SimpleLab Tap Score

Contact Us | SimpleLab Tap Score

author portrait
About The Author


Serving as the CCO at SimpleLab, Jorgen has been an integral part of Tap Score since its inception. With a passion for combating misinformation in the water industry, he is dedicated to empowering individuals with a clear understanding of the fundamentals of their drinking water. In his spare time, Jorgen enjoys creating immersive social experiences for Virtual Reality with his wife.
back to top