Understanding Water Quality Reports
A comprehensive guide to reading your Consumer Confidence Report, understanding EPA standards, and knowing what the numbers mean for your family's health
Last updated: March 2026 | Reading time: 12 minutes
Environmental Data Analysis
Expert Reviewed
This content has been reviewed by Dr. Sarah Chen, PhD, Environmental Science Advisor, to ensure accuracy and alignment with current environmental science standards.
Last reviewed: April 2026
What Is a Water Quality Report?
Every year, your local water utility is legally required to provide you with a Consumer Confidence Report (CCR), also known as an Annual Water Quality Report. This document, mandated by the EPA under the Safe Drinking Water Act, tells you exactly what's in your tap water and how it compares to federal safety standards.
According to the EPA, water utilities must deliver CCRs to customers by July 1st each year, covering the previous calendar year's data. These reports provide transparency about your drinking water quality, including any detected contaminants, their levels, and potential health effects.
However, many people find these reports confusing. They're filled with scientific terms, acronyms, and numbers that can be difficult to interpret. This guide will help you decode your CCR so you can make informed decisions about your water quality.
How to Get Your CCR:
- Check your mail between April and July
- Visit your water utility's website
- Call your water provider and request a copy
- Search the EPA's Drinking Water Watch database
- Check our water quality database for your city
What Water Quality Reports Show
Your CCR contains several key sections that together paint a complete picture of your water quality:
1. Water Source Information
Every CCR begins by identifying where your water comes from. Understanding your source helps you understand potential contamination risks:
- Surface water (rivers, lakes, reservoirs): More susceptible to agricultural runoff, industrial pollution, and seasonal variations. Typically requires more extensive treatment.
- Groundwater (wells, aquifers): Generally more protected from surface contamination but may contain naturally occurring minerals like arsenic or radon. Once contaminated, harder to remediate.
- Purchased water: Some utilities buy treated water from larger regional systems.
The EPA requires utilities to conduct Source Water Assessments to identify potential contamination sources near water supplies, such as gas stations, industrial facilities, or agricultural operations.
2. Detected Contaminants Table
This is the most important section of your report. It lists every regulated contaminant detected in your water during the reporting period. For each contaminant, you'll typically see:
- Contaminant name
- Level detected (often shown as a range or average)
- MCL (Maximum Contaminant Level - the legal limit)
- MCLG (Maximum Contaminant Level Goal - the health-based goal)
- Violation status (whether the MCL was exceeded)
- Likely source (where the contaminant comes from)
3. Violation Information
If your water system had any violations during the year, they must be clearly disclosed in the CCR along with:
- What contaminant or rule was violated
- Potential health effects
- What the utility is doing to correct the problem
- When the issue is expected to be resolved
4. Educational Information
CCRs must include standard language about:
- Vulnerable populations who may need to take extra precautions
- How to get more information from the water utility
- Definitions of key terms used in the report
Key Contaminants Explained
While the EPA regulates over 90 contaminants in drinking water, some appear in CCRs more frequently than others. Here are the most common categories:
Disinfection Byproducts (DBPs)
These chemicals form when disinfectants like chlorine react with organic matter in water. The most common DBPs are:
- Total Trihalomethanes (TTHMs): MCL of 80 ppb. Includes chloroform, bromodichloromethane, dibromochloromethane, and bromoform.
- Haloacetic Acids (HAA5): MCL of 60 ppb. A group of five acids formed during chlorination.
Health effects: Long-term exposure linked to increased cancer risk. The EPA considers these probable human carcinogens.
Lead
Lead typically enters water from corrosion of older pipes, solder, and fixtures rather than from the water source. The EPA's action level is 15 ppb, but the MCLG is zero because no level of lead is considered safe.
Health effects: Developmental delays in children, kidney damage, and cardiovascular effects in adults. Lead exposure is particularly dangerous for pregnant women and children under 6. Learn more in our Lead in Drinking Water Guide.
Nitrates
Nitrates come from fertilizer runoff, septic systems, and animal waste. The MCL is 10 mg/L (as nitrogen).
Health effects: Dangerous for infants under 6 months old, causing "blue baby syndrome" (methemoglobinemia). Pregnant women should also be cautious.
PFAS (Per- and Polyfluoroalkyl Substances)
Often called "forever chemicals," PFAS are a group of thousands of synthetic compounds used in non-stick cookware, firefighting foam, and water-resistant products. The EPA finalized new MCLs in 2024: 4 parts per trillion (ppt) for PFOA and PFOS individually.
Health effects: Linked to cancer, thyroid disease, immune system effects, and developmental issues. See our PFAS Guide for details.
Arsenic
Arsenic occurs naturally in groundwater, especially in Western states. The MCL is 10 ppb, though the MCLG is zero.
Health effects: Long-term exposure associated with increased cancer risk (skin, bladder, lung), cardiovascular disease, and diabetes.
EPA Standards and MCLs
Understanding EPA terminology is crucial for interpreting your water quality report correctly. Here are the key terms you need to know:
Maximum Contaminant Level (MCL)
Definition: The highest level of a contaminant legally allowed in drinking water.
How it's set: MCLs balance health protection with technical feasibility and cost. They're enforceable standards that water utilities must meet.
Important: MCLs are not purely health-based. They consider what's achievable with available technology and what's economically reasonable for water systems.
Maximum Contaminant Level Goal (MCLG)
Definition: The level of a contaminant at which no known health effects occur, including an adequate margin of safety.
Key difference from MCL: MCLGs are non-enforceable public health goals based solely on health considerations—not cost or feasibility.
Why the gap matters: When there's a significant difference between the MCL and MCLG, it means the legal limit allows contaminant levels that health experts consider potentially harmful. For example, lead's MCL action level is 15 ppb, but its MCLG is 0 because there's no safe level of lead exposure.
Action Level (AL)
Definition: The concentration that triggers additional treatment or other requirements.
How it works: Used for lead and copper, which enter water from home plumbing rather than the source. If more than 10% of tested homes exceed the action level, the utility must take corrective action.
Treatment Technique (TT)
Definition: A required treatment process intended to reduce the level of a contaminant.
When it's used: For contaminants where measuring exact levels isn't practical. For example, Giardia and Cryptosporidium use TT requirements because it's difficult to measure these parasites in finished water.
Common Units of Measurement:
- mg/L (milligrams per liter): Same as ppm (parts per million). 1 mg/L = 1 part per million.
- ug/L or mcg/L (micrograms per liter): Same as ppb (parts per billion). 1,000 ppb = 1 ppm.
- ng/L (nanograms per liter): Same as ppt (parts per trillion). Used for PFAS and other ultra-trace contaminants.
- pCi/L (picocuries per liter): Used for radioactive contaminants like radon and radium.
- NTU (Nephelometric Turbidity Units): Measures water cloudiness.
How to Read Your Local Report
Follow these steps to effectively analyze your CCR:
Step 1: Check for Violations First
Look for any section labeled "Violations" or any contaminant marked as exceeding its MCL. If violations exist, the report must explain:
- What was violated
- When it occurred
- What health effects are possible
- What's being done to fix it
Step 2: Compare Detected Levels to MCLs
For each contaminant, calculate what percentage of the MCL was detected:
(Detected Level / MCL) x 100 = Percentage of MCL
- Below 25%: Generally excellent
- 25-50%: Good, but worth monitoring
- 50-75%: Elevated; consider filtration for sensitive populations
- 75-100%: Concerning; filtration recommended
- Above 100%: Violation; take action
Step 3: Note the Gap Between MCL and MCLG
Pay attention to contaminants where the MCLG is significantly lower than the MCL, especially if your detected levels are high. This indicates the legal limit may not be fully protective.
Step 4: Check the Range of Detections
Reports often show both average levels and ranges. Wide ranges indicate inconsistent water quality throughout the year. If the maximum detection approaches or exceeds the MCL even occasionally, that's noteworthy even if the average is acceptable.
Step 5: Consider Multiple Contaminants Together
Having several contaminants at moderate levels may be more concerning than a single elevated contaminant. The cumulative effect of multiple chemicals isn't always reflected in individual MCLs.
Important Reminder:
Your CCR shows water quality as it leaves the treatment plant or enters the distribution system. Your tap water may differ due to your home's plumbing. Consider testing your tap water directly, especially for lead. See our Home Water Testing Guide.
What the Numbers Mean for Your Health
Understanding the health implications of your water quality results helps you make informed decisions:
Interpreting Contaminant Levels
Low Risk (Below 25% of MCL)
Contaminant levels well below regulatory limits with comfortable safety margins. Drinking this water long-term poses minimal known health risks for most people.
Moderate (25-50% of MCL)
Still meeting standards with safety margin. However, for contaminants with zero MCLGs (like lead), even these levels may warrant attention for sensitive populations including children, pregnant women, and immunocompromised individuals.
Elevated (50-75% of MCL)
Approaching regulatory limits. While technically compliant, some health experts recommend additional treatment at these levels, especially for contaminants linked to cancer or developmental effects. Consider point-of-use filtration.
High (75-100% of MCL)
Very close to regulatory limits with little safety margin. Seasonal variations could push levels above MCLs. Filtration is recommended, particularly for vulnerable populations. Monitor your CCR annually for changes.
Exceeding MCL
Your water system has violated federal standards. Follow any guidance from your utility. Install appropriate filtration or use alternative water sources until the issue is resolved. Contact your state drinking water program if you have concerns about the utility's response.
Special Considerations for Vulnerable Groups
The EPA and CDC identify certain populations who may need extra protection:
- Infants and young children: Particularly sensitive to lead, nitrates, and other contaminants. Use filtered water for formula preparation if any concerns exist.
- Pregnant women: Should avoid water with elevated lead, PFAS, or nitrates.
- Elderly individuals: May have reduced ability to metabolize certain contaminants.
- Immunocompromised individuals: Should be especially cautious about microbial contaminants.
Violations Explained
Not all violations are equal. Understanding the types helps you assess the seriousness of any issues:
Types of Violations
Health-Based Violations
Most serious. These occur when a contaminant exceeds its MCL or when required treatment isn't properly implemented.
- Maximum Contaminant Level (MCL) violations
- Maximum Residual Disinfectant Level (MRDL) violations
- Treatment Technique (TT) violations
Monitoring and Reporting Violations
Less immediate risk but concerning. These occur when utilities fail to test as required or don't report results properly.
- Failure to conduct required testing
- Late reporting of results
- Incomplete testing
While these don't necessarily mean your water is unsafe, they indicate the utility may not be monitoring adequately to ensure safety.
Public Notice Violations
Administrative but important. These occur when utilities fail to notify customers properly about water quality issues.
Public notification is critical because it ensures you can take action to protect your health when problems arise.
What To Do If Your System Has Violations
- Read the violation notice carefully. Understand exactly what's violated and potential health effects.
- Follow any immediate guidance. If a boil water notice is issued, comply until it's lifted.
- Consider alternative water sources. For serious violations, use bottled or filtered water for drinking and cooking.
- Install appropriate filtration. See our Water Filtration Guide for options.
- Monitor for updates. Check your utility's website or call for resolution updates.
- Contact your state. If you're concerned about the utility's response, contact your state's drinking water program.
What's NOT in Your Report
While CCRs are valuable, they have limitations you should understand:
Unregulated Contaminants
The EPA only requires testing for about 90 regulated contaminants, but thousands of chemicals can potentially appear in drinking water. Emerging contaminants not covered include:
- Many PFAS compounds: While PFOA and PFOS now have MCLs, thousands of other PFAS chemicals exist without standards.
- Pharmaceuticals: Prescription drugs, over-the-counter medications, and hormones are found in many water supplies but aren't regulated.
- Microplastics: No testing requirements or standards exist despite widespread presence.
- Many pesticides: Only a fraction of pesticides used in agriculture are monitored in drinking water.
Your Home's Plumbing
CCRs measure water quality in the distribution system, not at your tap. Your home's pipes, fittings, and fixtures can add contaminants, especially:
- Lead: From pipes installed before 1986 or lead solder
- Copper: From copper pipes, especially with corrosive water
- Bacteria: From biofilms in household plumbing
Real-Time Data
CCRs present annual data that may be months old by the time you receive it. Water quality can change based on:
- Seasonal variations in source water
- Treatment changes
- Infrastructure problems
- Contamination events
Recommendation:
For the most complete picture of your water quality, supplement your CCR with home water testing. This is especially important if you have older plumbing, are in a vulnerable population, or want to check for unregulated contaminants.
Taking Action Based on Your Report
Based on your CCR review, here's how to respond:
If your water quality looks good:
- Continue reviewing your CCR annually
- Consider testing for lead at your tap if you have older plumbing
- A basic carbon filter can improve taste if desired
If you see elevated levels (50-100% MCL):
- Test your tap water to confirm home levels
- Install point-of-use filtration appropriate for your contaminants
- Monitor CCRs for trends over time
- Consider whole-house filtration if multiple contaminants are elevated
If there are violations or you're concerned:
- Use bottled or filtered water for drinking and cooking
- Install reverse osmosis for comprehensive contaminant removal
- Contact your utility for more information
- Report concerns to your state drinking water program
- Consider having your water tested by a certified lab
Related Resources
- Common Water Contaminants Guide
- Home Water Filtration Guide
- Private Well Water Testing Guide
- Home Water Testing: Complete Guide
- PFAS Forever Chemicals Guide
- Water Quality by State
- Search Your City's Water Quality
Source: Information in this guide is based on EPA drinking water regulations, the Safe Drinking Water Act, and EPA guidance documents on Consumer Confidence Reports.