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 we hold the data to a health standard. We can't promise perfection, but we can promise a process—every number is traceable, reviewed against the authorities that set public-health guidance, and honest about what it does and doesn't know.
Every number traces to a named authority
We don't invent thresholds. Each figure traces back to a primary source: EPA (SDWIS and legal limits/MCLs), USGS (well and geology data), California OEHHA public health goals, ATSDR toxicological profiles, EWG, and the peer-reviewed literature. For every contaminant we publish both the legal limit and the health-protective guideline—so you see the regulatory floor and the target that actually protects a body.
Health guidance is reviewed, then reconciled to the source
Health guidance is reviewed against EPA, OEHHA, ATSDR, and WHO guidelines and the peer-reviewed literature. Before anything is published, the number is reconciled against its authoritative source—not paraphrased from memory. Per-group thresholds carry inline citations, so you can follow any value back to where it came from. Editorial review is handled by the CheckYourTap team.
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 legal
Legal limits weigh cost and feasibility alongside health— they answer “what can a utility reasonably meet?”, not “what protects a body?” We publish what protects a body, adjusted per population group—from newborns to elderly to pregnant and nursing family members—and even pets. Where a health-protective guideline is stricter than the legal limit, we show it.
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. Editorial review of health guidance is handled by the CheckYourTap team against the authorities above. 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.
Personalized Risk Assessment
Standard water quality reports treat every person the same. A 70-kg adult and a 4-kg newborn get the same “safe” threshold. That's not good enough.
CheckYourTap adjusts health guidelines based on who actually lives in your home. We calculate dose-adjusted exposure levels using body weight, water intake ratios, and vulnerability factors specific to each household member type:
Babies and young children receive proportionally higher exposure per kilogram of body weight. Pregnant women and nursing mothers face unique risks from certain contaminants that can cross the placental barrier or enter breast milk. Elderly adults may have reduced capacity to metabolize specific chemicals. Even pets have different sensitivity thresholds—cats, for example, are more vulnerable to certain heavy metals than dogs.
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
For private wells, we use USGS groundwater monitoring data and geological surveys—not direct testing of your specific well. Contaminant levels can vary significantly between neighboring wells depending on depth, geology, and nearby land use. A professional well water test is always recommended for definitive results.
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 for a free, personalized water quality report built from these data sources.
Check My Water