Understanding Water Quality Standards: HALs vs. MCLs
Ensuring the safety of your drinking water involves monitoring a variety of substances. To keep the public informed and protected, environmental agencies use two primary benchmarks to measure chemical safety: Health Advisory Levels (HALs) and Maximum Contaminant Levels (MCLs).
What is a Health Advisory Level (HAL)?
A HAL is a non-regulatory guidance value used when a chemical is detected in drinking water that does not yet have a formal federal standard.
- The Goal: To identify a concentration level that is virtually certain to cause no adverse health effects, even if the water is consumed over an entire lifetime.
- The Purpose: HALs serve as a “safety compass.” They provide the public and the Department of Environmental Protection (DEP) with essential data on the potential risks of emerging contaminants.
What is a Maximum Contaminant Level (MCL)?
An MCL is an enforceable legal standard established by the U.S. Environmental Protection Agency (EPA) under the Safe Drinking Water Act.
- The Goal: To set the highest level of a contaminant allowed in water delivered to users of a public water system.
- The Purpose: These are regulatory “speed limits.” The DEP uses MCLs to strictly oversee and manage the levels of chemicals in public water supplies to ensure long-term safety.
Key Differences at a Glance
| Feature | Health Advisory Level (HAL) | Maximum Contaminant Level (MCL) |
|---|---|---|
| Status | Informal Guidance | Enforceable Regulation |
| Authority | Based on available health data | Established by the EPA |
| Trigger | Used when no MCL exists | Standard for known contaminants |
| Function | Risk assessment and advice | Compliance and enforcement |