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8.2: EPA's Primary and Secondary Drinking Water Standards

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  • The 1974 Act

    Up until 1974, public drinking water supplies in the United States were monitored and regulated by state and local authorities. Lists of contaminants with their various concentrations could vary from state to state. As the chemical industry grew, these same state agencies noted the presence of more and new organic chemicals in public water systems. In order to standardize drinking water across the country, the Environmental Protection Agency (EPA) enacted the Safe Water Drinking Act of 1974.


    AFGE Thanks EPA Workers
    Figure \(\PageIndex{1}\): AFGE members and environmental activists participated in an event at the Washington, D.C. EPA headquarters to thank EPA workers for their work. Image used with permission (CC BY 2.0; AFGE).


    The 1974 act enabled the EPA to monitor and regulate public water systems that serve over 25 people. Implementation and enforcement of drinking water standards were still performed by each state. Regarding drinking water sources (surface and ground), the EPA and state agencies protect and monitor these as well. The EPA does not regulate private wells or bottled water in the United States. Well water monitoring is the responsibility of the owner. As for bottled water, the Food and Drug Administration (FDA) oversees this commodity by using EPA drinking water standards.


    Insert bottled water picture here with brief explanation of tap vs spring




    The first set of drinking water standards included only 22 chemicals and/or pathogens. EPA established to major types of contaminants: primary and secondary. The first of these types (primary) of contaminants are substances (examples could include Hg, As, and U) that can be toxic in small amounts. On the other hand, secondary contaminants are less toxic species (Fe and Zn) and would include cosmetic issues (color, taste, and odor) of drinking water.

    All primary contaminants have enforceable concentration values. For the majority of these pollutants, EPA lists specific limits by using the term Maximum Contaminant Level (MCL). If a water supplier exceeds a given MCL for a toxin, then fines and penalties could by imposed by the EPA. A few pathogens (Giardia Lamblia and Legionella) use Treatment Technique (TT) notation rather than numeric MCL concentrations. Water that contains any amount of these pathogens must be sanitized immediately with a standardized EPA procedure.


    Table \(\PageIndex{1}\): Exert of the EPA's Primary Drinking Water Contaminant Listing
    Primary Contaminant Classification


    MCL or TT1(mg/L) Potential Health Effects from Long-Term Exposure Above the MCL (unless specified as short-term) Sources of Contaminant in Drinking Water
    Giardia lamblia Microorganism zero TT3 Gastrointestinal illness (such as diarrhea, vomiting, and cramps) Human and animal fecal waste
    Thallium Inorganic 0.0005 0.002 Hair loss; changes in blood; kidney, intestine, or liver problems Leaching from ore-processing sites; discharge from electronics, glass, and drug factories


    In Table \(\PageIndex{1}\), a Maximum Contaminant Level Goal (MCLG) column is displayed for each of the two drinking water impurties. MCLG values are not enforced by the EPA. Instead, MCLG are suggested values that water suppliers should strive to meet. Every six years, the EPA reviews each primary contaminant with its MCL standard. During these times, they analyze data in regards to health risk assessment. If they choose to lower a MCL (smaller value) of a contaminant, then less health issues should occur. Unfortunately, reducing a concentration requires more technology which will cost the supplier and the consumer more money. By providing MCLG limits, the EPA encourages a water company to gradually work towards lowering a toxin's concentration.

    Primary Drinking Water Contaminants

    These types of toxins are classified into one of the six EPA classifications: microorganisms, disinfectants, disinfectant byproducts, inorganics, organics, or radionuclides. Primary contaminants are regulated because the have the capacity to do great harm to humans, plants, and animals. If a water distributor (must serve at least 200 homes) exceeds one of these mandated standards, then the EPA may impose a fine on the company.

    Clark Hill Dam.jpg
    Figure \(\PageIndex{2}\): Pretty picture. Image used with permission (CC BY; Elizabeth Gordon).

    Typically, concentrations of these contaminants are listed in parts per million. Metric amounts of a part per million are milligrams of the toxin per liter of sample.

    \[\text{ppm} = \dfrac{mg }{Liters }\]


    For extremely toxic substance, smaller units like parts per billion (ppb) might be used to express concentration.  Metric amounts of a part per billion are micrograms per liter of sample.  (or micrograms of contaminant per liter of water).


    \[\text{ppm} = \dfrac{mg }{Liters }\]




    mention differences between mcl and mclg. weird radionuclide units and asbestos......

    Amendment SDWA of 1986

    Amendment of SDWA of 1996