Our Data & Methodology
Transparency is part of the mission. Here's exactly how we collect, process, and present water quality data.
Scientific Rigor
How We Ensure Accuracy
This is a health resource, so every public comparison must be traceable and scoped. We cannot promise perfection, but we can show the process: preserve the source value and unit, distinguish health guidance from enforceable law, and abstain when a required contract is absent.
Every published number traces to a named authority
Health-protective references lead with sources including EWG and California OEHHA, supported where applicable by ATSDR, WHO, and peer-reviewed research. EPA is retained for measurements, legal limits, and regulatory context, and USGS for groundwater and geology. Every released comparison preserves its source, value, unit, and enforceability; if that evidence is absent, the UI abstains.
Public comparisons are release-gated
A reference comparison is publishable only when its exact value, unit, authority, comparator type, and release state pass the governed contract. Editorial claims and derived population or pet thresholds are held separately and remain dark until their exact source content and evidence are approved.
We show our confidence — and abstain when we can't be sure
Not all data is equal, so we label it. Every result carries a data-confidence signal—measured vs. area-estimate vs. geology-based. When the data is insufficient, we abstain: a contaminant is marked “untested / unknown,” never quietly assumed “safe.” And we never present a geology or proximity estimate as if it were a measurement of your specific water.
The standard is healthy, not merely legal
Enforceable limits and health-protective references answer different questions. Where an exact EWG or OEHHA reference is available in the same physical unit, we show that health comparison separately from EPA legal context. We do not turn a ZIP-associated record into an individual exposure or property-safety determination.
Who stands behind it
CheckYourTap is led by Alexander Snyder, Founder & Water Quality Data Lead, who runs the data pipeline that processes EPA, USGS, and EWG datasets into these reports. He reviews the health guidance against the authorities above. To be plain about it: he is also the person who writes it, so there is no second pair of eyes, and you should weigh it accordingly. We are a data and analytics team—not a medical practice—and we're honest about that distinction.
General information, not medical advice. CheckYourTap provides educational information about drinking water. It is not medical advice, a diagnosis, or a substitute for certified laboratory testing of your specific water. For health concerns, talk to your physician or pediatrician; for a definitive result, use a state-certified lab.
Data Sources
CheckYourTap aggregates water quality data from four authoritative sources. Each provides a different lens on what's in Connecticut's drinking water.
EPA SDWIS
Safe Drinking Water Information System
The federal compliance database. Contains violation records, contaminant levels from required testing, and water system boundaries for every public water system in the U.S.
Visit source →EWG Tap Water Database
Environmental Working Group
Goes beyond legal limits. Compiles utility testing data and compares results against health guidelines that are often stricter than federal standards.
Visit source →USGS NWIS
National Water Information System
Geological and groundwater data from monitoring wells across Connecticut. Essential for well water reports where no utility testing data exists.
Visit source →CT DPH
Connecticut Department of Public Health
State-level drinking water program data, including small system reports and Connecticut-specific advisories not always captured by federal databases.
Visit source →How We Process Data
The biggest challenge in water quality data isn't access— it's that every source uses different names for the same contaminant. The EPA calls it “Chromium (total)”, EWG lists “Total chromium”, and USGS uses a CAS number. Our pipeline reconciles all of these.
Our normalization pipeline:
- Bridge table matching — A lookup table maps every naming variant (display name, CAS number, detection key) to a single canonical contaminant identity.
- V3 normalization — All contaminants are assigned a standardized name key, category, and measurement unit, resolving conflicts between source databases.
- Health guideline comparison — Each contaminant is evaluated against multiple thresholds: the EPA legal limit (MCL), EWG health guideline, and where available, WHO and OEHHA standards. We display the strictest applicable guideline alongside the legal limit so you see both the regulatory floor and the health-protective target.
- Unit harmonization — Measurements reported in different units (ppb, ppm, mg/L, pCi/L) are converted to a common format for accurate comparison against guidelines.
Household Health Research
Water-health research is not one-size-fits-all. Age, pregnancy, nursing, health history, species, and breed can change which contaminant effects deserve attention.
CheckYourTap preserves research for the household groups people selected in the original experience:
The archived exposure tables and source-backed susceptibility warnings remain retained. The public report uses them for qualitative context, not invented pet-safe values or individualized diagnoses. Numeric population adjustments stay withheld until every source, transformation, and uncertainty assumption is independently governed. The public report does not calculate household risk. A certified property sample and an appropriate clinician or veterinarian are still required for individual health decisions.
Update Frequency
Our data pipeline refreshes quarterly from federal and state databases. Compliance testing by water utilities typically occurs on an annual or semi-annual cycle, so quarterly updates capture the most recent publicly available results. When significant contamination events or regulatory changes occur in Connecticut, we may update affected ZIP codes outside the regular cycle.
Limitations
We believe transparency means being honest about what our data can and cannot tell you.
Well water reports use geological estimates
If you are on a well, we show you groundwater wells in the USGS and state sampling record near your ZIP, plus geological surveys. That is not a test of your specific well, and the sampling record does not record whether a given well was somebody's drinking water. Contaminant levels vary significantly between neighboring wells depending on depth, geology, and nearby land use. A professional well water test is the only way to know what is in yours.
City water data is from compliance testing
Municipal water data comes from utility compliance reports, which reflect testing at treatment plants and distribution points. Your actual tap water may differ due to household plumbing (lead service lines, copper pipes) or localized distribution issues. These reports are not real-time measurements.
Some small systems have limited data
Very small public water systems serving fewer than a few hundred people may have limited testing history in federal databases. In these cases, your report may show fewer contaminants—not because they're absent, but because testing data is scarce.
Explore the Source Data
We encourage you to explore the databases we draw from. All of our source data is publicly available.
See it in action
Enter your ZIP code to review free ZIP-associated water-quality records built from these data sources.
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