Class A Surface Water Quality Standards

The following are paraphrased water quality standards for inland surface waters taken from Massachusetts General Laws, 314 CMR 4.05.  By designation, the Cambridge Water Supply is a "Class A" water source that shall also be an excellent habitat for fish, other aquatic life, and wildlife, and shall be suitable for primary and secondary contact recreation even if not allowed.

Dissolved Oxygen (DO)

  • No less than 6.0 mg/L in cold water fisheries and not less than 5.0 mg/L in warm water fisheries unless background conditions are lower;
  • Natural seasonal and daily variations necessary to protect existing and designated uses shall be maintained.



  • Shall not exceed 68°F (20°C) in cold water fisheries, unless naturally occurring;  
  • Shall not exceed 83°F (28.3°C) in warm water fisheries;
  • The rise in temperature due to a discharge shall not exceed 1.5°F (0.8°C); and
  • Natural seasonal and daily variations shall be maintained.



  • Shall be in the range of 6.5 - 8.3 (standard units) but no more than 0.5 units outside of the background range.



  • No single sample shall exceed 235 E. coli colonies per 100mL. 



  • Waters should be free from floating, suspended and settleable solids in concentration or combinations that would impair any use assigned to this class, that would cause aesthetically objectionable conditions, or that would impair the benthic biota or degrade the chemical composition of the bottom.


Color and Turbidity

  • Waters shall be free from color and turbidity in concentrations or combinations that are aesthetically objectionable or would impair any use of this class.


Oil and Grease

  • Waters shall be free from oil and grease, petrochemicals and other volatile or synthetic organic pollutants.


Taste and Odor

  • None other than from natural origin.