Data Sources & Methodology
Transparency about where our data comes from and how we process it
Primary Data Sources
EPA SDWIS Database
The Safe Drinking Water Information System (SDWIS) is the EPA's official database containing information about all public water systems in the United States. This includes violation data, enforcement actions, and compliance monitoring.
Visit EPA SDWISLead & Copper Rule Data
Lead and copper sampling results are collected under the EPA's Lead and Copper Rule (LCR). Water systems are required to monitor lead and copper levels at customer taps and report 90th percentile values.
Learn about the Lead & Copper RuleUSGS Water Quality Data
The U.S. Geological Survey provides comprehensive water quality data including hardness measurements. USGS conducts ongoing water quality assessments across the nation.
Visit USGS Water ResourcesOur Methodology
Data Collection
We aggregate data from multiple official sources and match it to cities based on the water systems that serve each area. When multiple water systems serve a city, we use population-weighted averages to provide representative values.
Violation Classification
EPA violations are categorized as either health-based or administrative. Health-based violations indicate exceedances of Maximum Contaminant Levels (MCLs), while administrative violations relate to monitoring, reporting, or other procedural requirements.
Water Hardness Classification
We use the standard USGS water hardness scale:
Soft
0–60 ppm
Moderately Hard
61–120 ppm
Hard
121–180 ppm
Very Hard
>180 ppm
Lead & Copper Thresholds
We compare reported 90th percentile values against EPA action levels: 15 ppb (parts per billion) for lead and 1.3 ppm for copper. Values approaching or exceeding these thresholds are flagged accordingly.
Update Frequency
Our database is updated periodically as new data becomes available from the EPA and state agencies. Violation data is typically updated quarterly, while water quality sampling results may be updated less frequently depending on the monitoring schedule for each water system.
Important Disclaimer
The information provided on Tapwater.org is for general informational purposes only. While we strive to keep our data accurate and up-to-date, we make no representations or warranties of any kind, express or implied, about the completeness, accuracy, reliability, or suitability of the information.
Water quality can vary significantly within a city depending on the specific water system, distribution network, and even the plumbing in individual buildings. For the most accurate information about your specific water supply, we recommend:
- Contacting your local water utility
- Reviewing your annual Consumer Confidence Report (CCR)
- Testing your own tap water with a certified laboratory
This website does not provide medical advice. If you have concerns about your water quality and health, please consult with a healthcare professional.