Compliance · US EPA
EPA National Drinking Water Standards
Drinking water: primary (MCL) and secondary (aesthetic), USA
The National Primary Drinking Water Regulations are the legally enforceable standards set by the US Environmental Protection Agency (EPA) under the Safe Drinking Water Act to protect public health. They establish maximum contaminant levels (MCLs), the highest concentration of a contaminant allowed in water delivered to the public, for microbial, chemical, and radiological hazards, including nitrate, arsenic, lead, disinfection byproducts, and turbidity. Alongside them, the secondary standards are non-enforceable guidelines for contaminants such as chloride, total dissolved solids, iron, manganese, and pH that affect taste, color, odor, and appearance rather than health.
The standard
What the EPA National Drinking Water Standards Are
Together the primary and secondary standards define what "safe" and "acceptable" drinking water means in the United States. The specific contaminants and their limits are given in the limit table on this page.
Limit values
EPA drinking water Limit Values
Every value US EPA publishes for the 5 parameters below, with its averaging period, as the standard states it.
Who it applies to
Who Must Comply
The regulations apply to public water systems: utilities and any operation that supplies water to the public, from large municipal networks to small systems serving schools, mobile-home parks, campgrounds, and workplaces. Their operators must sample and test on defined schedules, treat water to meet the MCLs, and report results to the state and to their customers. Engineers, treatment-plant operators, and environmental-health officials are responsible for demonstrating compliance, and an exceedance triggers public notification and corrective action.
Monitoring
How Monitoring Demonstrates Compliance
Some parameters (turbidity, pH, conductivity as a proxy for total dissolved solids, and specific ions such as nitrate and chloride) can be measured continuously in situ with a multiparameter sonde, giving operators an immediate picture of source and treated-water quality and early warning of a problem. A sonde on a Thiamis gateway streams these readings so that a turbidity spike or a shift in conductivity is caught as it happens, before a scheduled grab sample would reveal it. Other regulated contaminants, particularly trace metals, organics, and microbial indicators, still require laboratory analysis of collected samples for formal compliance. Continuous monitoring therefore supports operational control and early warning, while accredited laboratory testing provides the definitive record.
Recommended
best match-
Thiamis connects 1 instrument
A gateway that connects the third-party instruments you choose to the Aethair Platform.
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ChlorideNitrate (NO₃)pHTDSTurbidityYSI multiparameter water-quality sondes (Xylem): the current EXO platform and the legacy 6-series ('Sonde 6').
Swap for
Also measures 14 more
Dissolved Ammonia (NH₃)Ammonium (NH₄)Blue-Green AlgaeChlorophyllConductivityDissolved OxygenfDOM / CDOMORPSalinitySpecific ConductanceTSSWater Level / DepthWater PressureWater Temperature -
Who measures each parameter
| Parameter |  Aethair PRO |  Aethair IAQ | External |
|---|---|---|---|
| Nitrate (NO₃) | — | — | 5 instruments via Thiamis |
| Turbidity | — | — | 5 instruments via Thiamis |
| TDS | — | — | 5 instruments via Thiamis |
| Chloride | — | — | 5 instruments via Thiamis |
| pH | — | — | 5 instruments via Thiamis |
Devices
Devices That Cover EPA drinking water
How much of this standard one Aethair monitor covers, followed by the third-party instruments in the sensor catalog that measure its parameters. Each connects to Environet through a Thiamis gateway, which adds whatever the monitor leaves out.
Covers all 5 on its own
Solutions
Solutions Judged Against EPA drinking water
Water Quality Monitoring
Rivers, lakes, drinking water, and stormwater
Questions
EPA drinking water FAQ
What is a maximum contaminant level (MCL)?
An MCL is the highest concentration of a contaminant the EPA allows in water delivered by a public system, set to protect health while remaining achievable with available treatment. Each regulated contaminant has its own MCL, listed in the limit table on this page.
What is the difference between primary and secondary standards?
Primary standards are enforceable limits that protect health, such as those for nitrate, arsenic, and turbidity. Secondary standards are non-enforceable guidelines for contaminants that affect taste, color, odor, or appearance (chloride, total dissolved solids, iron, and pH among them), which utilities are encouraged but not required to meet.
Which drinking-water parameters can be measured continuously?
Turbidity, pH, conductivity (a proxy for total dissolved solids), temperature, dissolved oxygen, and, with ion-selective sensors, nitrate and chloride can be monitored continuously with a multiparameter sonde. Trace metals, organics, and microbial contaminants generally still need laboratory analysis for compliance.
How do I build a drinking-water monitoring setup?
Use a multiparameter sonde on a Thiamis gateway measuring turbidity, pH, conductivity, and temperature, adding ion-selective sensors for nitrate or chloride where relevant. Use the configurator to set up the sonde and pair continuous in-situ monitoring with your scheduled laboratory sampling.
Monitor Against EPA drinking water
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