How to Read Your Water Quality Report, Column by Column

How to Read Your Water Quality Report: The Short Answer

Your water quality report can list a sample above the legal limit while your utility is fully in compliance, and it can show a passing lead number while some homes tested high. Both are normal, and both are worth understanding. The report, officially called a Consumer Confidence Report (CCR), is the yearly summary your water utility has to send you, and most of what matters sits in one place: the table of detected contaminants. For each row, compare the level detected with the MCL, which is the legal limit. Check whether the violation column says yes. Then read the lead and copper rows on their own, because they're judged by a different yardstick.

Three things deserve a closer look: any violation, any result sitting close to its limit, and a lead 90th percentile over the action level, or any sampling sites that went over it. It's just as important to know what the report can't show. It describes your water system as a whole, not the water that comes out of your own faucet after it travels through your home's pipes.

Where to Find Your Report (and How Old the Numbers Are)

If you get water from a community water system, the EPA requires your supplier to send you a report each year by July 1. It might come in the mail, as a link printed on your bill, or as a page on the utility's website. If you can't find yours, call the utility or use EPA's CCR search tool.

Keep in mind that this year's report describes last year's water. Under federal rules for these reports, a report delivered by July 1 has to use data from the previous calendar year, or the most recent year before that. Some contaminants are allowed to be sampled less often than once a year. When that's the case, the table has to show the date and result of the most recent sampling, so glance at those dates before you treat a number as current.

Two situations work differently:

• Private wells don't get a report. According to the EPA, private well water isn't regulated by the federal government under the Safe Drinking Water Act, and most states don't regulate it either. If you're on a well, testing is how you find out what's in your water. Our well water testing guide walks you through it.
• Larger systems will report twice a year. EPA's revised report rule requires community water systems serving 10,000 or more people to send reports twice a year, with the new requirements starting in 2027. The same revision is meant to make the reports easier to read.

The Terms to Know Before You Read the Table

Reports have to define their key terms, and the federal rules spell out the wording. Here's what each one means for you.

One formatting quirk trips people up. The rules have the table show the MCL as a number of at least 1.0. That's why a limit written elsewhere as 0.010 mg/L usually appears in your report as 10 ppb. You'll also see NTU, a measure of water clarity, and pCi/L, a measure of radioactivity.

Reading the Detected Contaminants Table, Column by Column

Every utility lays its table out a little differently, but the rules require the same core facts for each regulated contaminant that was detected. Read each row from left to right.

The level detected

For most contaminants, this is the highest result at any sampling point. A few are judged on a running annual average instead, and for those the column shows the highest average at any monitoring location. That includes TTHM and HAA5, which the rules list as byproducts of drinking water disinfection.

That difference matters when you read the next column. For an averaged contaminant, the range can include single samples higher than the MCL even when the system is in compliance, because compliance is judged on the average.

The range

The range shows the lowest and highest results behind the headline number. A narrow range close to zero tells a very different story from a wide one that climbs toward the limit. If your utility serves separate areas fed by different water sources, the rules say it should break results out by service area, so find the column for the area you live in.

The MCL and MCLG columns

These sit side by side so you can see two gaps at once: how far a result is from the legal limit, and how far it is from the health goal. A result under the MCL is legally compliant. Where the MCLG is lower than the MCL, a result in between isn't a violation, but it's above the level defined as having no known or expected health risk.

The violation column

A "yes" here is the most important thing in the table. The report has to explain any violation in plain language, including how long it lasted, its potential health effects, and what the utility did to fix it. Read that explanation in full. Violations aren't only about contaminant levels, either. A utility that misses required monitoring or reporting has to disclose that too.

The likely source

This column names where the contaminant probably came from, to the best of the operator's knowledge. For lead and copper you'll usually see corrosion of household plumbing listed, and for many minerals, erosion of natural deposits. It helps you tell whether something starts in the source water or gets picked up on the way to your faucet.

Putting it together: reading a nitrate row

Here's how the columns work together on a real row. For nitrate, the federal rules list an MCL of 10 ppm and an MCLG of 10 ppm, with typical sources of fertilizer runoff, leaching from septic tanks and sewage, and erosion of natural deposits. Because the goal and the limit are the same number, there's no gap between them to think about. What you're really checking is how close the level detected and the top of the range come to 10 ppm. If the level detected is above 5 ppm, the report also has to include a note for people caring for infants, which is covered below. If you live near farm fields or a lot of septic systems, the source column is worth a second look.

Arsenic reads differently. Its MCL appears as 10 ppb, but its MCLG is zero. A detected level can meet the limit and still sit above the health goal, which is exactly why the MCLG column is there.

Why the Lead and Copper Rows Look Different

Lead mostly doesn't come from the treatment plant. The EPA explains that lead enters drinking water when plumbing materials containing lead corrode, and that lead service lines are typically the biggest source in homes that have them. So utilities collect tap samples from homes that are more likely to have lead plumbing, and these rows are built around an action level instead of an MCL.

For lead and copper, the report shows three things:

• The 90th percentile result from the most recent round of sampling
• The number of sampling sites that exceeded the action level
• The range of tap results

The 90th percentile is the number to focus on. It means 90 percent of the samples came in at or below that level. If more than 10 percent of tap samples go over the lead action level, the EPA requires the utility to take additional actions, such as educating the public about lead and, for some systems, further optimizing corrosion control. EPA's current lead action level is 15 parts per billion. Amended federal rules lower it to 10 ppb, and the updated requirements for these reports take effect November 1, 2027, so check which number your report uses. A 90th percentile between 10 and 15 ppb passes under today's level but would be over the amended one.

Two cautions before you relax about a passing number. A 90th percentile under the action level can still hide individual homes with higher results, which is why the report also lists how many sites went over. Your home may not have been sampled at all. The EPA also notes that there's no known safe level of lead in a child's blood. If your home has a lead service line or older plumbing, testing your own tap is the only way to know. Our guide to the Lead and Copper Rule explains the regulations behind these numbers.

The Unregulated Contaminants Section

Some reports have a separate section for unregulated contaminants. These are substances EPA requires some systems to monitor even though there's no MCL for them. The report shows the average and range detected, along with a short explanation, usually that the monitoring helps EPA learn where these contaminants occur and whether to regulate them.

A detection here isn't a violation, since there's no limit to break. It's still worth reading, because it shows what was found for substances that don't have a federal limit yet. Our explainer on the EPA Contaminant Candidate List covers how EPA decides which contaminants to study next.

Statements That Flag Something Worth a Closer Look

Some paragraphs only show up in a report when a result crosses a line or something specific happened. That makes them useful flags, even when there's no violation. Federal rules require them in these cases:

• Nitrate above 5 mg/L but below the MCL. The report has to include a note for anyone caring for an infant. Nitrate above 10 ppm poses a particularly high health concern for babies under 6 months old, so if you mix formula with tap water, the note suggests another water source or a talk with your health care provider. Our guide to nitrates in drinking water covers the options.
• Arsenic above 0.005 mg/L, up to the 0.010 mg/L MCL. The report has to include a short statement about arsenic. EPA's suggested wording notes that arsenic is known to cause cancer in humans, and that EPA's arsenic limit balances health effects against the cost of removing arsenic. So meeting the limit isn't the same as having no risk: the health goal for arsenic is zero. Our arsenic guide explains testing and removal.
• A Level 1 or Level 2 assessment. This means the utility had to study its system to identify potential problems and, if possible, find out why total coliform bacteria turned up. A Level 2 assessment is the more detailed version, triggered by an E. coli MCL violation or by coliform bacteria found on multiple occasions.
• Cryptosporidium results. If monitoring showed Cryptosporidium may be present in the source water or the treated water, the report has to summarize the results and explain what they mean.

What Your Report Can't Tell You

A clean report is good news. It just has limits worth keeping in mind:

• It describes the system, not your tap. Your own service line, pipes and fixtures can still add lead or copper before water reaches your glass.
• It looks back. The data comes from last year or earlier, so it won't reflect anything that's changed since.
• It covers what was monitored. The table lists what turned up under required testing. It can't speak to substances the utility wasn't required to test for.

What to Do After You've Read It

1. Ask about anything unclear. Your report lists a phone number for the utility, and it's there for questions like yours. EPA's Safe Drinking Water Hotline is another option at 800-426-4791.
2. Test your own tap if something stood out. A violation, a lead exceedance, a result near its limit, or older plumbing in your home are all good reasons. Crystal Quest® offers a City Water Test for homes on municipal water, and our guide to testing your water at home compares the options.
3. Choose treatment for what you actually found. A filter reduces the contaminants it's designed for, so start from your report and your tap results rather than a guess. If you're still deciding whether you need one, our list of signs you need a water filter is a good next read.

Frequently Asked Questions

Why does my report list contaminants if there's no violation?

Because some level of contaminants is normal. The rules require reports to say that drinking water, including bottled water, may reasonably be expected to contain at least small amounts of some contaminants, and that their presence doesn't necessarily mean the water poses a health risk. What matters is the level compared with the MCL and MCLG.

Can I shower if my report shows a lead action level exceedance?

Generally, yes. The EPA says bathing and showering should be safe for you and your children even if the water contains lead over the action level, because human skin doesn't absorb lead in water. It adds that individual circumstances may vary, and highly corrosive water may call for extra precautions, so follow any specific instructions from your utility or health department.