MCLG (Maximum Contaminant Level Goal)
An MCLG is a non-enforceable, health-based goal set by EPA at the contaminant concentration at which no known or anticipated adverse health effect occurs and which allows an adequate margin of safety — defined under 40 CFR § 141.2 and authorized by SDWA § 1412(b)(4).
Where you'll see it on a CCR
Every CCR that reports a regulated contaminant must list both the MCLG and the enforceable MCL side by side. The table typically has three columns: MCLG, MCL, and the system's measured level. When your system's result falls between the MCLG and the MCL — or below both — that context matters to readers. The MCLG column tells them what EPA considers the health-protective target; the MCL column tells them what the law actually requires.
If your system's result equals or beats the MCLG, say so plainly. If it sits between the MCLG and the MCL but is still in compliance, that's also worth a sentence of plain-language explanation — readers notice the gap and will ask about it.
Why MCLG can be lower than MCL
The MCLG is what EPA would set if cost and treatment technology were irrelevant. The MCL is what EPA can actually require given feasibility constraints. SDWA directs EPA to set the MCL as close to the MCLG as is feasible; the gap between the two reflects the limits of current treatment, not a judgment that the difference is safe.
For contaminants that are known or probable carcinogens — including lead and copper at the tap, PFOA, and PFOS — EPA sets the MCLG at zero. There is no demonstrated safe level for these substances. The MCL for lead, for example, is not zero; it reflects the lowest level achievable across the range of water systems. An MCLG of zero does not mean any detected amount will cause immediate harm, but it signals that EPA found no threshold below which risk disappears entirely.
This distinction matters on your CCR: if a contaminant has an MCLG of zero and your system detected any amount, readers may need that context explained. The MCL compliance status is what matters legally, but the MCLG tells the fuller health story.
California sets its own parallel goal called a PHG (Public Health Goal), administered by OEHHA. PHGs often equal or undercut federal MCLGs, which is why California CCRs list three columns — PHG, MCL, and measured level — rather than two.
Related terms
- CCR (Consumer Confidence Report) — the annual water quality report that must disclose MCLG and MCL for each regulated contaminant detected
- Glossary — full index of CCR terminology
- MCL (Maximum Contaminant Level) — the enforceable federal drinking water standard derived from the MCLG
- PHG (Public Health Goal) — California's analog to the MCLG, set by OEHHA; often more stringent than the federal MCLG
Citations
- 40 CFR § 141.2 (definitions, including MCLG): https://www.law.cornell.edu/cfr/text/40/141.2
- SDWA § 1412(b)(4), codified at 42 U.S.C. § 300g-1(b)(4): https://www.law.cornell.edu/uscode/text/42/300g-1
- 40 CFR § 141.151–141.156 (CCR Rule, Subpart O): https://www.law.cornell.edu/cfr/text/40/141.151