# Understanding Drinking Water Standards: Health Advisory Levels (HALs) vs. Maximum Contaminant Levels (MCLs)

- Link: https://moran.rocks/health-advisory-levels-vs-maximum-contamination-levels/
- Published: 2026-04-17T14:49:52-04:00
- Author: Nicholas Moran

# 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)**.

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### 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.

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### 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 |