Silent Spring Institute

Water Quality Indicators


Recommended water quality indicators 

Massachusetts Department of Environmental Protection (MassDEP) recommends that you test for nitrate and total coliform at least once per year. 


The U.S. EPA's standard is 10 parts per million (ppm or mg/L). Nitrate levels above 10 ppm are harmful to infants. Nitrate levels above 1 ppm show impact from human activities and may indicate the presence of other contaminants. Common sources of nitrate in private wells include septic systems or fertilizers. 


Total coliform & fecal coliform

The presence of total coliform is a sign that harmful bacteria, such as E. coli, may be present. A follow-up test for fecal coliform should be conducted. Fecal coliform are harmful bacteria found in human and animal waste. A positive test on a fecal coliform test requires immediate action. 



Common water quality indicators

Regular, but less frequent testing of your water's acidity and hardness may provide additional information to you about the quality of your water. MassDEP recommends that you test pH and hardness at least every 10 years. 

pH (acidity) 

The U.S. EPA's recommended range of pH (acidity) is 6.5 to 8.5. Water with a pH value below 6.5 can corrode pipes and release harmful lead and copper from plumbing.



Hardness is a measure related to the amount of dissolved minerals (calcium and magnesium) in water. Hard water is not harmful, but hard water can cause mineral buildup in appliances and fixtures that heat water.