How to read your water quality report

What the report is

Every community water system in the country has to send its customers a water quality report each year. EPA calls it a Consumer Confidence Report, or CCR. It arrives by July 1 and covers the previous calendar year. Many utilities now deliver it as a link on your bill rather than a printed mailer.

Starting in 2027, utilities serving 10,000 or more people must send a second report by December 31, with an update on the first half of the year.

The report has to name your water's source, list every regulated contaminant that was detected, explain any violation and what the utility did about it, and give the EPA Safe Drinking Water Hotline: 1-800-426-4791.

The detected contaminants table, column by column

This table is the heart of the report. Most utilities lay it out roughly like this:

Column	What it means
Contaminant	What was measured. Only detected contaminants have to be listed.
Level detected	The number that counts for compliance. Often an average, not the highest sample.
Range	The lowest and highest results across the year.
MCL	The legal limit. Enforceable.
MCLG	The health goal. Not enforceable.
Violation	Yes or no.
Likely source	Where the contaminant typically comes from.

Read across each row and ask two questions. Is the level under the MCL? That tells you whether the utility met the law. Is it above the MCLG? That tells you whether it is above the level where EPA expects no risk at all.

The definitions every report must print, in EPA's own words:

• MCL: "The highest level of a contaminant that is allowed in drinking water. MCLs are set as close to the MCLGs as feasible using the best available treatment technology."
• MCLG: "The level of a contaminant in drinking water below which there is no known or expected risk to health. MCLGs allow for a margin of safety."
• Action level: "The concentration of a contaminant which, if exceeded, triggers treatment or other requirements which a water system must follow."
• Treatment technique: "A required process intended to reduce the level of a contaminant in drinking water."

The units

Reports switch units from row to row, which makes comparing hard.

• ppm, parts per million, is the same as milligrams per liter (mg/L). Nitrate, copper and fluoride are usually in ppm.
• ppb, parts per billion, is micrograms per liter (µg/L). Lead and arsenic are usually in ppb. 1 ppm is 1,000 ppb.
• ppt, parts per trillion, is nanograms per liter (ng/L). PFAS are in ppt. 1 ppb is 1,000 ppt.

The PFOA legal limit of 4.0 ppt is the same as 0.004 ppb. A report that prints it in ppb can make a real result look like nothing.

Lead and copper work differently

Lead and copper get their own small table. Instead of an average, the report shows the 90th percentile: the level that 90 percent of the homes sampled were at or below. Instead of an MCL, it shows an action level. If more than 10 percent of samples exceed the action level, the utility has to act.

EPA's health goal for lead is zero. Lead usually enters water from service lines, solder and faucets between the main and your glass, so the utility's number describes its system, not your kitchen. The lead page has the current action level and the changes scheduled for it.

Unregulated contaminants

When EPA requires a utility to monitor a contaminant that has no limit yet, the report must show the average and range it was detected at. This is where PFAS results from EPA's UCMR 5 program often appear, sometimes with no MCL column at all, because many PFAS have no federal limit.

The violations section

A violation means the utility missed a limit, a treatment requirement, or a monitoring or reporting deadline. They are not equal. A health-based violation means the water itself fell short. A monitoring or reporting violation means a sample was missed or filed late. The report must say what the utility did to fix it.

What the report cannot tell you

It describes the utility's system, not your tap. Your own service line, plumbing and fixtures can add lead and copper that no utility sample captures. If you have an older home, a certified laboratory test of your own tap is the only way to know.

The faster way

TapBuff rewrites your utility's report from EPA's own data, measured against both yardsticks, with the filter standard for anything above a health goal.