Your Water Quality Report Is Out. Here Is What the Numbers Mean.

It's July, which means that the deadline just passed for your water utility to send you a report on what its required testing found in your drinking water last year. The report is called the Consumer Confidence Report (or CCR) and every community water system has to provide one by July 1. If you didn't get it in the mail, you can find the report by searching your utility's name and CCR. If your home is on a well, you'll need to order your own testing, because private well owners are responsible for testing and treating their own water.

I have spent much of my career working with these reports and breaking them down. CCRs are a "right-to-know" tool for the public to understand what's in their drinking water, but they're full of regulatory jargon that most consumers don't understand. Some of the numbers listed in the CCR are unenforceable public-health goals. Some are enforceable legal limits that also account for treatment technology, measurement limits, and cost.

While the CCR has obvious blind spots in scope and can be confusing at times, the pool of test results is something that would cost an individual thousands of dollars to recreate for their home if they chose to. The goal of this article is to help you make use of the test results found in the CCR, add context to the regulatory jargon, and give you a better way to understand your water.

What the CCR includes, and what it leaves out

Many people believe the CCR is a complete audit of your water, but that's an oversimplification because water providers test what they're required to test for. The requirements are set by the Safe Drinking Water Act (SDWA), which includes just over 90 regulated contaminants, plus narrow testing requirements for a small set of unregulated contaminants. That testing does not cover many of the things that show up in the news, including microplastics and most pharmaceuticals, because new contaminants can take years or decades to work their way through the regulatory process once they're identified as harmful. The other thing that sometimes surprises people is that a CCR is a look back at the previous year's testing results, not what's coming out of your tap today.

• Detected level: What was found in your water
• MCLG: Health-only goal
• MCL: Legal limit
• AL: Trigger for lead and copper

MCLG: The "Health-Only" Level

The way to think about the Maximum Contaminant Level Goal (MCLG) is that it's a health-only level, meaning EPA sets it based on public-health risk, without considering treatment cost or feasibility. The MCLG, by definition, is set at the level where there are no known or expected health effects caused by the contaminant, with a margin of safety built in. For some carcinogens, the MCLG is zero because the EPA has not identified a safe nonzero dose.

One thing that can confuse people is that even though the MCLG represents the health-based goal for a contaminant in drinking water, it is an unenforceable goal, not a regulatory limit that water systems must meet. Because the MCLG is a science-based health-only goal, I recommend comparing detected results to the MCLG first, then looking at the MCL to see whether the water system met the legal standard.

MCL: The Legal Limit

Unlike the MCLG, which is an unenforceable goal, the Maximum Contaminant Level (MCL) is the enforceable regulatory limit that water systems are required to meet. EPA establishes MCLs with three criteria in mind: health effects, cost, and system-scale treatment feasibility. EPA sets each MCL as close to the MCLG as feasible, while balancing the other factors.

An example of how this plays out is in the case of arsenic, a known carcinogen that can contaminate groundwater in areas where the bedrock has naturally-occurring arsenic. The "health-only" MCLG for arsenic is zero (because there's no safe nonzero dose), but the legally-enforceable MCL is 10 parts per billion (ppb). A utility delivering water at 9 ppb of arsenic is in full compliance, and its CCR will show no violation, even though scientific literature shows that arsenic is associated with health problems (including cancer) at levels lower than that.

AL: The Lead and Copper Rule Trigger

Lead needs to be regulated differently than contaminants like arsenic or PFAS, because lead contamination comes from leaching in pipes, not the water supply itself (where MCLs are applied). Instead of testing water leaving the treatment plant for lead, EPA uses a metric called an Action Level (AL), based on the 90th percentile of samples collected from higher-risk homes. The AL for lead is 15 ppb currently, but is scheduled to change to 10 ppb in 2027 as a result of the Lead and Copper Rule Improvements. The testing protocol works by collecting first-draw water samples from higher-risk homes across the system. If more than 10 percent of those samples exceed the AL, the utility must take action, which can include making changes to corrosion control technologies, replacing lead service lines, and stepping up public education.

With lead results, it's easy to get lost in the statistics at the system-wide level, so it's important to take a step back and remember:

1. The Action Level (15 ppb now, changing to 10 ppb) was not developed from any kind of toxicological study, and was never meant to be a safe threshold. The MCLG for lead is zero, because there is no safe nonzero dose, especially for children. The way I think about the AL is more of a process-control trigger for the water system's corrosion-control program.
2. The 90th percentile system-wide measurement doesn't tell you anything about the lead level in your home. Your home's level will depend largely on whether or not your service line (the underground pipe that connects your home to the city's water main) and internal plumbing components contain lead. This means that your home could have a high lead result, while your neighbor tests at zero. The only way to know for sure is by getting your water tested by an accredited laboratory.

How to Read and Interpret Your CCR

A CCR can be a pretty long document, and you don't need to read most of it. I tell people to skip straight to the data tables, and do the following.

• Before digging into the numbers, do a quick scan to see if any contaminants had results that exceeded the MCL. These should be specifically called out. If a contaminant exceeds the legal limit, you should pay close attention to it.
• Contaminants with an MCLG of zero. These are the contaminants where EPA has not identified any safe dose so they should be your first priority, mostly carcinogens like arsenic, benzene, certain PFAS like PFOA and PFOS, and certain disinfection byproducts. If any contaminants with an MCLG of zero were detected in the report, those rows deserve a closer look.
• Results for any other contaminant where the MCL and the MCLG are different. While only a few contaminants fall into this category (e.g. chlorite), it's worth a quick check because like the previous category, these are instances where EPA had to set the legal limit higher than the health-only limit for feasibility or cost reasons.
• Lead and Copper Rule Results, which are often found in a separate table. It's important to find the specific LCR table, because those tests are conducted at taps, not at the treatment plant. Because lead contamination is specific to the individual home, the numbers in the CCR shouldn't be taken at face value. That said, especially if you live in an older building or don't know if your service line or plumbing components contain lead, the CCR could give you an idea of what others are seeing in their home, so you can decide if it's worth ordering a lead test for your home. Sometimes cities provide this service to residents for free.
• Unregulated Contaminant Monitoring Rule Results. UCMR discloses concentrations of a limited number of unregulated contaminants that EPA has flagged as a concern and requires certain water systems to monitor them as part of a study to determine how frequently they occur in public water systems. These results will generally be found separate from the main data. It's important to understand that it's not possible for a UCMR contaminant to create an MCL violation, because there is no MCL yet. This can cause confusion in scenarios where you hear about the toxicity of certain contaminants, but water providers say that the water meets all regulatory standards.

CCRs come out every July, and starting in 2027, systems serving 10,000 or more people will send a second one by December 31, so you'll get more updates. Once you've read a few, the real payoff is comparing them: a single CCR is a snapshot, but the year-over-year trend in your own utility's numbers can tell you more than the results from a single year. And it pays off outside the report, too: the next alarming water headline gets a lot easier to put in context, and you'll probably end up the go-to water expert in your family.