Safe Drinking Water Act: National Primary and Secondary Drinking Water Regulations

The Safe Drinking Water Act and Why It Matters

The Safe Drinking Water Act (SDWA), first passed in 1974 and significantly amended in 1986 and 1996, is the federal law that authorizes the U.S. Environmental Protection Agency (EPA) to set standards for public drinking water quality. As a licensed water operator, you work directly within the framework this law creates. Violating SDWA requirements is not a paperwork problem — it can harm public health and result in legal penalties for both the utility and the operator personally. Your state drinking water program operates under EPA primacy, meaning your state has been granted authority to enforce standards that are at least as stringent as federal rules.

National Primary Drinking Water Regulations (NPDWRs)

Primary drinking water regulations are legally enforceable standards that protect public health. They apply to public water systems and set limits or controls on contaminants that may pose a health risk when present in drinking water. There are three main tools EPA uses under the NPDWRs:

Maximum Contaminant Level (MCL): The MCL is the highest concentration of a contaminant that is legally allowed in drinking water delivered to any user of a public water system. MCLs are set as close to the MCLG as is feasible, meaning as close as current technology and cost allow. MCLs are expressed in milligrams per liter (mg/L) or, for very low concentrations, micrograms per liter (µg/L). Exceeding an MCL triggers a mandatory response by the operator, including notifying the state and, depending on the contaminant and level, issuing a public notice.

Maximum Contaminant Level Goal (MCLG): The MCLG is the non-enforceable, health-based target — the level at which no known or anticipated adverse health effects occur, with an adequate margin of safety. MCLGs are set without regard to cost or technical feasibility. For contaminants such as lead and certain carcinogens, the MCLG is set at zero because no safe exposure level has been established. The MCLG guides EPA in setting the MCL but is not itself a legal limit you can violate.

Treatment Technique (TT): For some contaminants, it is not technically or economically practical to measure them reliably at very low levels in every sample. Instead of an MCL, EPA establishes a required treatment technique — a specific process or operational standard the system must follow. The best examples are Giardia lamblia and Cryptosporidium, two protozoan pathogens. Because these organisms are difficult and expensive to measure in every water sample, EPA requires systems to achieve specific levels of filtration and disinfection removal and inactivation credit rather than test for the organisms themselves. Turbidity limits and disinfection log-inactivation requirements are examples of treatment technique rules.

Key Regulated Contaminants You Must Know

The EPA National Primary Drinking Water Regulations table lists contaminants across several categories. The categories you will encounter most on state operator exams include:

• Microbiological: Total coliform, E. coli, turbidity (as a treatment technique indicator)
• Inorganic chemicals: Nitrate, nitrite, arsenic, fluoride, barium, chromium
• Disinfection byproducts (DBPs): Total trihalomethanes (TTHMs), haloacetic acids (HAA5)
• Disinfectant residuals: Limits on chlorine, chloramines, and chlorine dioxide
• Lead and copper: Regulated under the Lead and Copper Rule as action levels (not traditional MCLs)
• Radionuclides: Combined radium, gross alpha, uranium, beta particles

Always use the current EPA table — values are updated when the science changes. For the exam and for practice, memorize the MCL values for the most common contaminants (nitrate at 10 mg/L as nitrogen, nitrite at 1 mg/L as nitrogen, arsenic at 0.010 mg/L, and total coliform rules based on percentage of positive samples).

National Secondary Drinking Water Regulations (NSDWRs)

Secondary standards are non-enforceable federal guidelines relating to the aesthetic qualities of drinking water — taste, odor, color, and appearance. Examples include pH, hardness, iron, manganese, and chloride. States may choose to adopt secondary standards as enforceable rules. As an operator you should know these values because customers notice them even when water is safe to drink.

Operator Safety Considerations

Regulatory compliance has a direct safety dimension. When an MCL exceedance is detected for contaminants such as nitrate (linked to methemoglobinemia in infants), lead, or microbial pathogens, operators must act quickly and accurately. Delayed reporting is a regulatory violation. Always wear appropriate PPE — chemical-resistant gloves and eye protection — when collecting and handling water samples for laboratory analysis. Follow your facility's sampling protocols exactly; improper sample collection can produce false results that either mask a real violation or trigger an unnecessary public notice. Lockout/tagout procedures apply whenever you access sample taps or equipment associated with treatment processes.

Putting It Together

When you receive a sample result, the decision sequence is straightforward: (1) identify the contaminant and its applicable standard — MCL, action level, or treatment technique; (2) compare the result to that standard; (3) if the standard is exceeded or not met, follow your state-approved response protocol, notify the state agency within the required timeframe, and document everything. Your operator license depends on knowing these numbers and acting on them correctly.