Environment

Is Your Drinking Water Safe? How to Check Water Quality Data

Feb 28, 2026 · 9 min read · Deep Seer Team

In 2014, the city of Flint, Michigan switched its water source to the Flint River without proper corrosion treatment. Within months, lead levels in children's blood spiked. Residents complained about discolored, foul-smelling water for over a year before state officials acknowledged the crisis. The data showing dangerous lead levels existed in government databases the entire time — the problem was that nobody outside the state was looking at it.

You do not need to wait for a crisis to check your water. The federal government publishes water quality data from thousands of monitoring stations, and your local utility is legally required to publish annual testing results. Here is how to find and interpret that data.

The Two Major Data Sources

USGS National Water Information System (NWIS)

The U.S. Geological Survey operates over 10,000 active monitoring stations across the country, measuring streamflow, water level, and water quality in rivers, lakes, and groundwater. NWIS data is accessible through waterdata.usgs.gov. These stations measure raw environmental water quality — what is in the rivers and aquifers before treatment — making them essential for understanding the source water that feeds into drinking water systems.

EPA Water Quality Portal (WQP)

The Water Quality Portal at waterqualitydata.us aggregates data from USGS, the EPA's STORET database, and state environmental agencies into a single searchable interface. It contains over 400 million water quality measurements from more than 900,000 monitoring locations. You can search by location, parameter, date range, and data provider. The WQP covers both ambient (environmental) water quality and some treated water measurements.

Deep Seer pulls from the Water Quality Portal API, allowing users to query monitoring stations within any geographic bounding box and visualize contaminant readings on a 3D globe alongside facility discharge data and health outcome statistics.

Your Annual Water Quality Report

Every community water system serving more than 15 connections is required by the EPA's Consumer Confidence Report (CCR) rule to publish an annual water quality report. Your utility must mail it to you or provide a direct URL by July 1 each year. If you have not seen yours, search for your utility's name plus "water quality report" or "CCR" — most are published as PDFs on the utility's website.

The CCR lists every contaminant detected in your treated water, the level found, the EPA's Maximum Contaminant Level (MCL), and the Maximum Contaminant Level Goal (MCLG). The MCL is the legally enforceable limit. The MCLG is the non-enforceable health goal — often stricter than the MCL. When a detected level exceeds the MCL, the utility is in violation and must notify customers.

Contaminants That Matter Most

Lead

Lead contamination usually comes not from the water source but from the pipes between the water main and your tap. Lead service lines, lead solder, and brass fixtures can all leach lead into water, particularly when water chemistry is corrosive (low pH, low mineral content). The EPA's action level for lead is 15 parts per billion (ppb), measured at the 90th percentile of homes sampled — meaning if more than 10% of sampled homes exceed 15 ppb, the system must take corrective action. The MCLG for lead is zero. There is no safe level of lead exposure, particularly for children.

To check for lead specifically in your home, request a free or low-cost lead test kit from your water utility. Many utilities have been required to inventory their service line materials under the EPA's 2024 Lead and Copper Rule Improvements — ask your utility whether your service line is lead, galvanized, copper, or unknown.

PFAS (Per- and Polyfluoroalkyl Substances)

In April 2024, the EPA finalized the first-ever national drinking water standard for PFAS — a class of synthetic chemicals used in nonstick coatings, firefighting foam, and food packaging that have been linked to cancer, immune suppression, and developmental harm. The new MCLs are 4 parts per trillion (ppt) for PFOA and PFOS individually, with a hazard index approach for mixtures of PFHxS, PFNA, HFPO-DA (GenX), and PFBS.

Four parts per trillion is extraordinarily low — roughly equivalent to four drops of water in an Olympic-sized swimming pool. Many water systems will need to install granular activated carbon or ion exchange treatment to meet these standards. Check your CCR for PFAS results. If PFAS is not listed, your system may not have tested for it yet — the compliance deadline for large systems is 2029.

Nitrates

Nitrate contamination primarily affects agricultural areas where fertilizer runoff enters groundwater. The EPA MCL is 10 mg/L (ppm) for nitrate measured as nitrogen. Levels above this can cause methemoglobinemia ("blue baby syndrome") in infants under six months, a condition where nitrate interferes with the blood's ability to carry oxygen. If you are on a private well in an agricultural area, annual nitrate testing is essential — private wells are not covered by EPA regulations.

Coliform Bacteria and E. coli

Total coliform bacteria are indicator organisms — their presence suggests that disease-causing organisms could also be present. Under the Revised Total Coliform Rule, any detection of E. coli in treated water is a violation that triggers immediate public notification and corrective action. A single positive E. coli sample means the treatment system has failed to eliminate fecal contamination.

Disinfection Byproducts

Chlorine used to disinfect water reacts with organic matter to form trihalomethanes (THMs) and haloacetic acids (HAAs). The MCLs are 80 ppb for total THMs and 60 ppb for HAA5. Long-term exposure above these levels is associated with increased cancer risk. Systems that draw from surface water with high organic content (lakes, rivers) tend to produce more disinfection byproducts than groundwater systems.

Finding Your Nearest Monitoring Station

Go to waterqualitydata.us and click "Advanced" search.
Enter your location using either a bounding box (latitude/longitude coordinates) or a county/state selection.
Under "Characteristic," enter the parameter you are interested in — for example, "Lead" or "Nitrogen, nitrate (NO3) as nitrogen."
Set a date range. Recent data (last 5 years) is most relevant.
Click search. Results include the station name, location coordinates, sampling dates, measured values, and detection limits.

For a faster visual approach, the USGS National Water Dashboard at dashboard.waterdata.usgs.gov shows active monitoring stations on a map. Click any station to see its real-time and historical data.

How to Interpret Readings

When reviewing water quality data, keep these principles in mind:

Compare to the MCL, not just the MCLG. Many contaminants have an MCLG of zero (lead, many carcinogens), which no treatment system can achieve. The MCL is the enforceable standard and represents what the EPA considers an acceptable risk-benefit balance given treatment technology costs.
Look at trends, not single samples. A single high reading could be a sampling artifact. Three consecutive quarters with elevated readings indicate a real problem.
Check detection limits. If a lab reports "non-detect" for PFAS with a detection limit of 10 ppt, and the MCL is 4 ppt, the non-detect does not mean the water is safe — it means the lab could not detect levels below 10 ppt. The contaminant could be present at 9 ppt and still show as non-detect.
Distinguish source water from treated water. Environmental monitoring data (USGS, WQP) measures raw water before treatment. Your CCR measures treated water at the tap. High contaminant levels in source water do not necessarily mean your treated water is unsafe — but they do indicate what your treatment plant must remove.

What to Do If Levels Are Concerning

If your CCR shows contaminant levels near or above MCLs:

Request independent testing. State-certified labs offer water testing for $20-$200 depending on the panel. Your state health department maintains a list of certified labs.
Contact your utility. Utilities are required to respond to customer inquiries about water quality. Ask specifically what treatment they use for the contaminant of concern and whether they are planning upgrades.
File a complaint with your state drinking water program. Every state has a primacy agency that enforces the Safe Drinking Water Act. Complaints trigger inspections.
Consider point-of-use treatment. NSF-certified activated carbon filters remove many organic contaminants including PFAS and THMs. Reverse osmosis systems remove lead, nitrates, and most dissolved contaminants. Match the filter to the specific contaminant — no single filter removes everything.
If you are on a private well, you are entirely responsible for your own water quality. Test annually for bacteria, nitrates, and pH at minimum, and test for lead, arsenic, and PFAS if you are in an area with known contamination sources.

Clean drinking water is not something you should have to take on faith. The data exists. The monitoring stations are running. The annual reports are published. The gap is not in the data — it is in the number of people who know how to find it and what it means. Now you do.