How to Read a Municipal Water Quality Report

Table of Contents

• What a Municipal Water Quality Report Is and Why It Exists
• Finding Your Local Report and Confirming It Matches Your Address
• Step-by-Step: Reading the Contaminant Results Table
  • A Worked Example, Column by Column
  • Reading a Row in Order
  • What the Footnotes Change
• Understanding ppm, ppb, and Other Units on the Report
• Non-Detects, Averages, Ranges, and Legal Limits Versus Health Guidance
• What the Report Does Not Tell You About Water at Your Tap
• Putting Your Water Test Results Explained Into Action
  • If the Report Lists a Violation
  • If Lead Is a Concern
  • If a Contaminant Is Above a Health Guideline but Below the Legal Limit
  • If You Notice Unusual Taste, Odor, or Staining
  • A Short Checklist for Any Finding
• Frequently Asked Questions

What a Municipal Water Quality Report Is and Why It Exists

Last Updated: November 8, 2026

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If your water comes from a city or county system, your water supplier must send you a yearly water quality report on what is in it.

Public water systems in the United States must produce these reports under federal drinking water rules (the EPA). The Environmental Protection Agency explains the program and what suppliers must include on its EPA Consumer Confidence Report guidance.

A typical report covers where your water comes from (river, reservoir, or groundwater wells), the treatment steps such as filtration and disinfection, and a table of contaminants the utility tested for with the levels it found.

• Source of water: rivers, lakes, reservoirs, or wells
• Treatment steps: filtration and disinfection
• Contaminant results: detected levels and legal limits

Finding Your Local Report and Confirming It Matches Your Address

Most utilities post the CCR on their website, usually in a section called "Water Quality" or "Consumer Confidence Report." Some mail a printed copy with your bill.

Before you read it, confirm the report year (a report can be almost a full year old) and the water system's name and service area.

• Look for the system's name and PWSID (public water system ID) on the cover.
• Compare the service area listed to your street or neighborhood.
• Check the report year against the current date.

If the service area does not match your address, contact the utility before relying on the numbers.

Step-by-Step: Reading the Contaminant Results Table

The contaminant table is the core of the report. Most tables follow the same column pattern, so once you learn the layout you can read any utility's report.

1. Find the contaminant name. Rows are usually grouped by type, such as microbiological, inorganic, or radioactive.
2. Read the detected level. This is the highest level found or the average, depending on the test.
3. Check the range. Some tables show the lowest and highest results from samples taken that year.
4. Compare to the limit. Look for the MCL (maximum contaminant level), the legal limit for that substance.
5. Read the likely source. Many tables explain where the contaminant comes from, such as farm runoff or pipe corrosion.
6. Look for a violation note. If the level went above the limit or the utility missed a required test, the report should say so.

A Worked Example, Column by Column

Here is a typical row as it appears in many reports, followed by what each column means in plain language. The numbers below are illustrative, not from any specific utility.

• Contaminant: the substance tested. Nitrate, lead, and TTHM are common entries.
• MCL: the enforceable legal limit. For lead, the table shows an action level (AL) instead because lead is regulated through a treatment technique.
• MCLG: the health-based goal, not enforceable. For lead it is zero because no safe level is established.

Reading a Row in Order

Take the nitrate row. The MCL and MCLG are both 10 ppm, so the legal limit and health goal line up.

Now the lead row. The action level is 0.015 ppm and the MCLG is zero. The level found is 0.004 ppm, with a range from non-detect to 0.011 ppm. The highest sample is below the action level, so the system is in compliance.

What the Footnotes Change

A single number can mean different things depending on the footnote. Look for these notes before you compare rows:

• "Highest single sample" versus "annual average": the same samples can produce very different reported values.
• "90th percentile": used for lead and copper. It means 90 percent of samples were at or below that value, not that every tap tested at that level.
• "Running annual average": used for disinfection byproducts. It smooths out seasonal spikes, so a single high quarter may not show up.

Watch out: a result below the MCL does not always mean the water is free of that substance. Check whether the table shows a detected level or only a non-detect entry, and read the footnote to see whether the number is a single sample, an average, or a percentile.

Understanding ppm, ppb, and Other Units on the Report

Reports use small units because contaminants show up in tiny amounts. Three of them appear most often:

• ppm (parts per million): one part of contaminant in one million parts of water. It is the same as milligrams per liter (mg/L).
• ppb (parts per billion): one part in one billion parts of water. It is the same as micrograms per liter (µg/L).
• pCi/L (picocuries per liter): used for radioactive substances such as radon or radium.

A helpful comparison: one ppm is about one drop of water in a 42-gallon barrel, and one ppb is about one drop in a 42,000-gallon tank.

Watch the units closely. A value listed as 5 ppb is one thousand times smaller than 5 ppm, even though the numbers look similar.

Many people also see the term "NTU" in the turbidity section. NTU measures how cloudy the water is. Lower numbers mean clearer water.

Non-Detects, Averages, Ranges, and Legal Limits Versus Health Guidance

A few terms in the report confuse many readers.

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Non-detect (ND) means the test did not find the substance above its detection limit. It does not always mean zero.

Average is the mean of the results from samples taken that year.

Range shows the lowest and highest results from the samples.

Sampling frequency tells you how often the utility tested.

Legal limits and health guidance are not always the same thing:

• Legal limits (MCL): enforceable standards set by the Environmental Protection Agency. Utilities must keep water below them.
• Health-based goals (MCLG): the level at which no known health risk is expected. These are not enforceable and are often set at zero for some contaminants.

Water below the legal limit meets the standard. Whether it is the level you want for your household is a separate question.

What the Report Does Not Tell You About Water at Your Tap

The utility report describes water leaving the treatment plant and moving through the distribution system. It does not describe the water inside your home after it passes through your pipes, fixtures, and water heater.

Several things can change water between the main and your faucet:

• Older plumbing may add lead or copper.
• Water sitting in pipes for long periods can change in quality.
• Hot water heaters can concentrate some minerals.

The report also cannot tell you about hardness, iron staining, or sulfur odors unless the utility tested for them.

If you have concerns about your own plumbing or taste and odor, consider testing water at the tap.

Putting Your Water Test Results Explained Into Action

Once you have read the report, decide what to do next.

1. No action needed. All results are below the MCLs, there are no violations, and nothing in the report concerns you.

2. Watch and follow up. Some results are close to a limit, or the report mentions rising levels.

3. Respond promptly. The report lists a violation, a level above a limit, or a health advisory.

If the Report Lists a Violation

A violation means the system did not meet a federal requirement, either because a contaminant exceeded its limit or because required testing or reporting was missed. The report must describe the violation, the potential health effects, and what the utility is doing about it.

• Read the violation notice first, before the rest of the table. It tells you whether the issue is ongoing or resolved.
• Follow any instructions about boiling water, using bottled water, or avoiding certain uses. These instructions are specific to the contaminant and the population affected.
• Call the utility and ask three questions: Is the violation still active? What is the current level? When will the next test result be available?

If Lead Is a Concern

Lead is regulated through an action level rather than an MCL, and the health goal is zero. A report showing lead below the action level is not a guarantee of zero lead at your tap, because the sample is drawn from a set of homes and the result is a 90th percentile value.

• Check whether your home has a lead service line. Many utilities publish a service line inventory, and you can ask the utility directly.
• Run cold water for a short period before drinking or cooking if water has been sitting in the pipes, especially in older homes.
• Consider a certified filter for lead if your home has lead plumbing or a lead service line. Look for a filter certified to NSF/ANSI Standard 53 for lead reduction (the EPA).

If a Contaminant Is Above a Health Guideline but Below the Legal Limit

Some reports include health-based guidance values lower than the enforceable MCL. A result can be legal and still above a guideline, which is common for disinfection byproducts and contaminants with a nonzero health goal.

• Read the health information section for that contaminant. It explains the known risks and the populations most sensitive to them.
• Ask the utility whether the level is stable, rising, or seasonal. A single year above a guideline is different from a multiyear trend.
• Consider a home treatment option matched to the contaminant. Carbon filters address many disinfection byproducts and taste and odor issues, while reverse osmosis addresses nitrate and some metals. Match the device to the finding rather than buying a general-purpose system.

If You Notice Unusual Taste, Odor, or Staining

Taste, odor, and staining are not always covered by the CCR, because many are aesthetic rather than health-based. Chlorine taste, sulfur odor, iron staining, and hardness are common complaints a report may not flag.

• Check whether the issue is hot or cold water only. Hot-water-only odors often point to the water heater.
• Ask the utility whether the system recently changed its disinfectant or source water. Seasonal switches can change taste and odor.
• Test your tap water for the specific issue you notice, such as hardness, iron, sulfur, or chlorine, rather than relying on the system-wide report.

A Short Checklist for Any Finding

• Call the utility and ask what the result means for your household.
• Ask whether the issue is at the source, the treatment plant, or the pipes.
• Test your own tap water if you suspect a problem inside your home.

If your results raise questions about hardness, iron, sulfur, or chlorine taste, a professional water analysis can show what is happening at your own fixtures. Water Treatment Systems offers free water analysis; contact us to learn more and request your analysis.

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