Drinking Water Standards and Maximum Contaminant Levels

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Our 148,000+ public water systems here in the U.S. provide drinking water to 90% of the population. All of these community water systems, regardless of location, must abide by federal regulations for water quality that are enforced by federal law. Each state also has the option to set its own standards for specific drinking water contaminants as long as they are at least as stringent as existing national standards. 

Despite these layers of protection, hundreds of dangerous drinking water contaminants affect millions of Americans like us each year. Dozens of common contaminants are completely unregulated while others are legally allowed in community water systems at worrisome levels. If you’re wondering how our public drinking water supplies are regulated, then this is for you.

National Drinking Water Standards Established In 1974.

The Safe Drinking Water Act (SDWA) was enacted to establish national quality standards for all public water supplies in the United States. These national standards are set and monitored by the U.S. Environmental Protection Agency (U.S. EPA) and are enforced by federal law.

Some of the first contaminants the EPA regulated under the SDWA included arsenic, chromium, fluoride, lead, nitrate, mercury, and selenium.

As the EPA further monitored health data into the 90s, inorganic chemical contaminants like antimony, beryllium, cadmium, nitrite, asbestos, and thallium each earned regulations.

Today, the EPA routinely assesses water sources for harmful contaminants and implements regulations if necessary to protect public health. For more information,  visit www.EPA.gov.

National standards include:

  • Water-testing schedules. All public water supplies are tested regularly. 

  • Water-testing methods. Consistent protocols apply to all testing.

Drinking water quality control. Legal limits set by the EPA determine the maximum amount of specific contaminants allowed in public water supplies. These standards impact disinfection and treatment techniques to help protect drinking water quality.

What Are MCLs?

The EPA has established legal limits called Maximum Contaminant Levels (MCLs) for over 90 contaminants in public drinking water. According to the EPA, MCLs are established at levels that are scientifically determined to be safe and achievable through the implementation of the most advanced technology available to water treatment facilities.

How Does the EPA Determine MCLs?

When the EPA reviews the health effects data for a given contaminant and determines a regulation is needed, the agency will establish a non-enforceable public health goal called a maximum contaminant level goal (MCLG).

According to the EPA, MCLGs are “the maximum level of a contaminant in drinking water at which no known or anticipated adverse effect on the health of persons would occur, allowing an adequate margin of safety.”

The EPA will then consider the feasibility of removing the contaminant from public water supplies to determine an enforceable standard that becomes the contaminant’s official MCL.

While the EPA’s goal is to establish the MCL as close to the MCLG as possible, your safety is not the only factor for setting legal limits; it’s just one of three key considerations:

Key considerations include:

  • Human health

  • Testing technology

  • Cost

Are MCLs Ever Updated?

The EPA reviews existing regulations every six years and revises them if appropriate.

The truth is MCLs haven’t been updated for the majority of contaminants in almost 50 years.

In the context of public health, the latest data, studies, and research reveal many MCLs are often too high to protect us from the health hazards associated with specific contaminants. For example, lead has an MCL of 15 parts per billion (ppb), but no amount of lead in drinking water is safe.

What About New & Unregulated Contaminants?

No, the EPA does not have standards for all contaminants detected in tap water. More than 160 unregulated contaminants have been found in our public water supplies. In addition, new contaminants regularly emerge from the surface water that fills our water supplies, byproducts created during treatment, aging and damaged infrastructure such as galvanized pipe corrosion, and more. Said differently, hundreds of dangerous contaminants can legally be floating in your water right now, at any level, without repercussion.

How The EPA Handles Emerging Contaminants:

The Safe Drinking Water Act requires the EPA to publish a Contaminant Candidate List (CCL) every five years. The EPA then decides whether or not to monitor these contaminants and eventually regulate them based on three key factors:

  • Adverse health effects.

  • Likelihood of contamination at levels of concern.

  • If regulation offers a “meaningful opportunity” for health risk reductions.

Recent examples include the cancer-linked ‘forever chemicals’ PFOA and PFOS in the fourth edition of the contaminant candidate list (CCL4). The EPA determined these chemicals posed a significant enough health risk to warrant national primary drinking water regulations. In addition, the agency plans to thoroughly assess additional PFAS chemicals in line with the most up-to-date scientific evidence.

Another well-known contaminant, BPA (an endocrine disruptor that affects fetuses and children), is officially under surveillance in CCL5 as a possible candidate for maximum contaminant level regulation. Learn more about the dangers of BPA in drinking water here.

States, Territories, & Authorized Tribes Can Establish Their Standards Under Certain Conditions

The Safe Drinking Water Act (SDWA) gives individual states, territories, and authorized tribes the opportunity to set and enforce their own standards for public water supplies as long as they are at a “minimum as stringent as EPA national standards.” To be clear, a state cannot set a drinking water standard that is less protective than its national standard. 

For example, New Jersey and New Hampshire lowered their statewide arsenic limits to 5 ppb. That’s just half of the EPA MCL of 10 ppb. In other words, these states have set a standard twice as protective as the nationwide standard due to health concerns. 

States can also develop standards for unregulated contaminants. For example, there is no legal limit for perchlorate. However, California has set a statewide MCL of 0.006 mg/L for the chemical. 

How these standards work:

  • All national standards apply to all public water supplies, even if states, territories, or authorized tribes have created their own standards.

  • States, territories, and authorized tribes can set and enforce their own standards under one condition: State standards must be at least as protective as national standards.

If national standards do not exist for specific contaminants, states, territories, and authorized tribes can develop their own standards.

What Are Health Guidelines For Water Quality?

The Environmental Working Group (EWG), an American non-profit organization that specializes in the research and advocacy of various public health threats including drinking water pollutants, has its own set of “health guidelines” for water quality. These guidelines are designed to protect public health. Unlike EPA legal limits, they are just recommendations that are not enforceable by law.  

Health Guidelines vs Legal Limits (MCLs):

As mentioned earlier, the EPA openly admits cost and technology are both factors in determining national standards / legal limits. That’s why the EWG reviews the latest science, data, and research to create their own standards, also known as “health guidelines.” 

EWG health guidelines are notbased on political or economic compromise”; a clear shot at EPA legal limits. The group adds: “Too often, legal limits are based on what can be achieved cheaply, with little or no regard for public health. And water treatment facilities in many communities … are outdated, overloaded or underfunded.” 

Remember, the majority of regulated contaminants haven’t received updated MCLs in decades—even though studies have shown many contaminants can be dangerous below legal limits.

The EWG points out that EPA legal limits are often hundreds of times higher than the health standards recommended by scientists and public health agencies.

Plus, nationwide standards are non-existent for hundreds of contaminants proven to pose health risks. We shared a few examples of these unregulated contaminants earlier, including perchlorate, BPA, and PFAS.  

What About Well Water?

According to the CDC, more than 15 million U.S. households rely on a private well for drinking water.

Private well water is not regulated by the EPA, Centers for Disease Control and Prevention (CDC), Food and Drug Administration (FDA), or any other government agency. Instead, the property owner is responsible for maintaining water quality.

Given wells collect groundwater that can be littered with fertilizer, fuel, pesticides, and other dangerous contaminants, it’s crucial owners get their well water tested regularly. But, again, the EPA offers several resources to point people who own property with private wells in the right direction here. Next up, let’s talk about bottled water.

What About Bottled Water?

The FDA regulates bottled water because it’s classified as food. Many of the FDA’s bottled water regulations match the EPA’s National Primary Drinking Water Regulations. Therefore, bottled water can contain the same contaminants as tap water, including unregulated and emerging contaminants. 

Plus, bottled water is riddled with its own dangers. Harmful shreds of plastic, known as microplastics, can tear up your stomach, plastic bottles can leach chemicals into the water, and overused plastic bottles are breeding grounds for bacteria. In short, bottled water is typically no cleaner or safer than drinking water provided by public water utilities. In most cases, bottled water is virtually the same water that pours out of your tap.

The Bottom Line

Federal, state, and local government agencies are responsible for the safety of our public water supplies. However, contaminants detected below legal limits—and therefore deemed safe by national standards—can still be dangerous. Remember, legal limits have not been updated in decades for the majority of regulated contaminants, and therefore they likely do not account for new science and data. Plus, hundreds of dangerous contaminants already detected in our public water supplies remain unregulated today. 

The best thing you can do to protect yourself and your family is to invest in a water filter that virtually eliminates contaminants known to plague our public drinking water sources. Click here to find the right filter for you.

Wondering What’s In Your Water?

Our free database linked here compiles all of the test results from our public water supplies so you can see exactly what’s in your water, how it can affect you, and how to best protect yourself and your family. As you’ll see, we’ve included the legal limit for each regulated contaminant as well as EWG health guidelines for every contaminant to give you a complete and transparent assessment of your water.


1. Information about Public Water Systems https://www.epa.gov/dwreginfo/information-about-public-water-systems#:~:text=There%20are%20over%20148%2C000%20public,or%20on%20an%20occasional%20basis.

2. Summary of the Safe Drinking Water Act https://www.epa.gov/laws-regulations/summary-safe-drinking-water-act#:~:text=(1974),above%20ground%20or%20underground%20sources.

3. National Primary Drinking Water Regulations https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations

4. EWG Standards Cut Through Compromises on Drinking Water Quality https://www.ewg.org/news-insights/news/ewg-standards-cut-through-compromises-drinking-water-quality

5. Causes and Effects of Lead in Water https://www.nrdc.org/stories/causes-and-effects-lead-water

6. State of American drinking water https://www.ewg.org/tapwater/state-of-american-drinking-water.php

7. Basic Information on the CCL and Regulatory Determination https://www.epa.gov/ccl/basic-information-ccl-and-regulatory-determination

8. SDWA Evaluation and Rulemaking Process https://www.epa.gov/sdwa/sdwa-evaluation-and-rulemaking-process

9. Regulatory Determination 4 https://www.epa.gov/ccl/regulatory-determination-4

10. CCL 5 Chemical Contaminants https://www.epa.gov/ccl/ccl-5-chemical-contaminants

11. State-Specific Water Quality Standards Effective under the Clean Water Act (CWA) https://www.epa.gov/wqs-tech/state-specific-water-quality-standards-effective-under-clean-water-act-cwa

12. Drinking Water Regulations https://www.epa.gov/dwreginfo/drinking-water-regulations

13. Dep Adopts New Mercury, Arsenic Standards https://www.nj.gov/dep/newsrel/2004/04_0130.htm

14. N.H. Becomes Second State To Sharply Lower Arsenic Limit In Drinking Water https://www.nhpr.org/nh-news/2019-07-15/n-h-becomes-second-state-to-sharply-lower-arsenic-limit-in-drinking-water

15. Maximum Contaminant Levels and Regulatory Dates for Drinking Water U.S. EPA vs California https://www.waterboards.ca.gov/drinking_water/certlic/drinkingwater/documents/ccr/mcls_epa_vs_dwp.pdf

16. Environmental Working Group https://en.wikipedia.org/wiki/Environmental_Working_Group

17. Introducing EWG Standards https://www.ewg.org/research/introducing-ewg-standards

18. Private Ground Water Wells https://www.cdc.gov/healthywater/drinking/private/wells/index.html

19. Private Drinking Water Wells https://19january2017snapshot.epa.gov/privatewells_.html

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