Well Water Contamination

There are many ways drinking water may become contaminated. Contamination may result from biological (bacteria, viruses, etc.) or from chemical sources. Chemical contamination can occur from natural sources, such as arsenic leaching from rock formations, or can result from human activities, such as agricultural or industrial operations, or from improper chemical disposal at home.

Signs of Well Water Contamination

Many substances that contaminate water can be noticed without chemical testing. Below are some of the most easily observed water conditions. Recognizing these conditions can help prevent more serious problems and provide direction regarding what types of laboratory analysis may be needed.


  • Scale, scum or encrustation from calcium or magnesium salts in water Unclear/turbid water from dirt, clay salts, silt or rust in water
  • Green stains on sinks or faucets may be caused by high acidity
  • Brown or black stains may be due to high levels of Manganese (Mn) and/or Iron (Fe).
  • Blue water or blue deposits on fixtures may be due to high levels of copper (Cu), especially if coupled with corrosive water.
  • Orange-red water or stains on sinks dishwasher or clothes in wash may be due to dissolved iron in water
  • Cloudy, colored or frothy water may be due to suspended particulates, poorly working pump or filters, sewage waste or detergents.
  • Plumbing system with older lead pipes, fittings or solder joints may cause lead (Pb), cadmium (Cd) and/or zinc to leach from lead pipes, fittings or solder joints.
  • Corroding water heater or metal pipes may be due to corrosive water.


  • Salty or brackish taste from high sodium content in water.
  • Alkali/soapy taste from dissolved alkaline minerals in water Metallic taste from acidity or high iron content in water.
  • Chemical taste from volatile or semivolatile organic compounds (VOCs) or pesticides.


  • A rotten egg odor can be from dissolved hydrogen sulfide gas or certain bacteria in water. Turpentine odor in water may be due to methyl tertiary butyl ether (MTBE).
  • A detergent odor and water that foams when drawn could be seepage from sewage disposal tanks into your groundwater well.
  • A musty/earthy smell or rotting flesh smell may be from decaying organic matter in water.
  • Chlorine smell may be due to excessive chlorination.

 The best way to know if your water is safe is to have it tested by a laboratory certified for bacteriological and/or chemical analysis.

For More Information

Contaminants Found in Groundwater
Source: U.S. Geological Survey.

Ground Water and Drinking Water
Source: Environmental Protection Agency.

Well Owner Maintenance Practices
Source: National Groundwater Association.

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Public Health Division
County of Sonoma
Business Hours
Monday – Friday
8:00 AM – 4:00 PM
Office Location
625 5th Street
Santa Rosa, CA 95404
38.441823, -122.7137698

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