The KnowYourH2O Surface Water Quality Index (WQI) Calculator is a free online tool for individuals, community groups, educators, and watershed organizations exploring the quality of streams, rivers, lakes, and reservoirs. It summarizes entered water-quality measurements in a score that can help communicate monitoring results.

Open the Surface Water Quality Index Calculator or read the calculator user guide before entering your data.

Understanding the Water Quality Index Score

The calculator is described as based on the National Sanitation Foundation (NSF) Water Quality Index, with adaptations for its online implementation. Consult the user guide for the calculation method, supported inputs, and any differences from the original NSF methodology.

The calculator presents results on a 0–100 scale using these letter-grade categories:

• A, Excellent: 90–100
• B, Good: 70–89
• C, Medium: 50–69
• D, Bad: 25–49
• F, Very Bad: 0–24

These are the calculator’s reporting categories. A surface-water WQI score is not a determination that water is safe to drink and does not replace testing for contaminants relevant to drinking-water use.

Using Complete and Partial Monitoring Data

The calculator supports partial data entry, including submissions with as few as one parameter, and up to nine parameter categories. More complete data provides a broader assessment of the conditions measured. A score based on a single parameter describes a much narrower set of conditions and should not be interpreted as a comprehensive assessment of water quality.

The parameter categories described for the tool include dissolved oxygen (percent saturation), bacterial indicators, pH, biochemical oxygen demand (BOD), temperature change, phosphorus, nitrogen, turbidity, and total solids. Check the guide for the exact measurement, units, and reporting basis required for each entry.

Do not assume that fecal coliform and E. coli, phosphate and total phosphorus, nitrate and total nitrogen, or turbidity and Secchi depth are interchangeable. Use an alternative measurement only where the calculator guide explicitly supports it, and follow its instructions for any conversion or adjustment.

When comparing sites or tracking changes over time, document the parameters used, sampling methods, units, dates, and site conditions. Scores based on different parameter sets or sampling methods should not be treated as directly equivalent.

Citizen Science and Watershed Monitoring Applications

• Flexible data entry: Use available measurements for educational exploration or monitoring, while reporting the limitations of incomplete data.
  
  
• Location-aware reporting: The tool includes options for site coordinates or map-based location selection, actual monitoring data versus training/test data, and downloadable PDF reports. Review the guide before submitting data intended for the shared database.
  
  
• Field use: Access the web tool on a mobile device when collecting or reviewing monitoring information.
  
  
• Practical applications: Use it to support watershed monitoring, surface-water assessments, citizen science projects, STEM activities, and discussions about non-point source pollution and ecosystem health.

Community Participation and Shared Data

The project is intended to help citizen scientists, students, educators, and watershed organizations communicate monitoring results and contribute to a shared Citizen Science Global Surface Water Quality Database and Map. Actual monitoring submissions and training/test entries serve different purposes; choose the appropriate option when using the tool.

The accompanying infographic presents reported participation and submission totals for 2023–2026. These figures should be treated as the infographic’s dated project statistics rather than independently verified, continuously updated totals.

For watershed groups, a consistent reporting framework can make results easier to discuss with communities and decision-makers. Meaningful comparisons still depend on comparable inputs, sampling practices, and documentation. Groups interested in participating can also explore the project’s Global Directory of Citizen Scientist Teams, Conservation Groups, and Watershed Organizations.

The tool is part of KnowYourH2O’s outdoor educational resources for surface-water monitoring and is developed and maintained through the KnowYourH2O / Keystone Clean Water Team grassroots effort.

Start with the Calculator and User Guide

Use the free Surface Water Quality Index Calculator to explore your measurements. For sampling, data-entry requirements, and interpretation, consult the Surface Water Quality Index Calculator User Guide.

Learn More About Your Drinking Water

Surface-water monitoring and drinking-water testing answer different questions. To learn more about your drinking-water quality, consider a DIY testing kit or an informational laboratory analysis through the NTL Mail Order Testing Service for well water or city water. Select testing appropriate to your water source and the contaminants of concern; no single kit or panel measures every possible contaminant.

Want to learn more about the water in your home? Order Our Drinking Water, our educational booklet for well-water and city-water users.

Other Websites

• Know Your H2O
• B.F. Environmental Consultants
• Carbon County Groundwater Guardians
• Keystone Clean Water Team (Donate)

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