Water Quality Standards

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The term water quality can be difficult to define depending on the type of water being defined (e.g., surface water, ground water, drinking water, etc.) and the parameters of its use (e.g., agricultural or industrial use, for drinking, etc.). Water quality parameters vary in scope but in general, we are most concerned with health issues that may arise from contaminants (primary or secondary effects) in drinking water and water used in recreation. Below are some tables that define certain water quality parameters from various resources.

EPA Maximum Contaminant Levels (MCLs)

The information below was gathered from the US EPA website.[1] These values are for drinking water, not untreated surface/ground water.

Contaminant MCL (ppm) Noticeable Effects above MCL Possible Sources
arsenic (As) 0.010 skin damage; circulatory problems erosion[2]; runoff from orchards
barium (Ba) 2 increase in blood pressure drilling waste discharge; metal refineries; erosion
cadmium (Cd) 0.005 kidney damage erosion; galvanized pipes; metal refineries; batteries & paints
chromium (Cr) 0.1 allergic dermatitis steel and pulp mills; erosion
fluoride (F-) 4.0 bone disease; mottled teeth in children erosion; fertilizer plants
lead (Pb) 0.015 kidney issues; high blood pressure; retarded growth in children old pipes; erosion
mercury, inorganic (Hg) 0.002 kidney damage erosion; refineries; landfills
nitrate (NO3-) 10 severe illness/death in infants agricultural runoff; sewage; erosion

EPA Secondary MCLs

The information below was gathered from the US EPA website.[3] These values are for drinking water, not untreated surface/ground water.

Contaminant Secondary MCL (ppm) Noticeable Effects above MCL
aluminum (Al) 0.05–0.2 colored water
chloride (Cl-) 250 salty taste
fluoride (F-) 2.0 tooth discoloration
iron (Fe) 0.3 rusty color; sediment; metallic taste
manganese (Mn) 0.05 black to brown color; bitter metallic taste
pH 6.5 – 8.5 (not in ppm units); low pH gives bitter metallic taste; high pH gives soda taste
sulfate (SO42-) 250 salty taste
TDS 500 hardness; colored water; salty taste

Further Reading


  1. ^ Table of Regulated Drinking Water Contaminants. US EPA. https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations; accessed 02/01/2016.
  2. ^ In this case, erosion means the erosion of natural mineral deposits that contain the metal.
  3. ^ Table of Secondary Drinking Water Standards. US EPA. https://www.epa.gov/dwstandardsregulations/secondary-drinking-water-standards-guidance-nuisance-chemicals; accessed 02/01/2016.