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The Water Confidence Index (WCI): Its Development and Construction

April 26, 2021

Objective

To develop an environmental composite index—Water Confidence Index (WCI)—that measures and ranks the performance of large U.S. public water systems (PWS) based on environmental compliance and truthful reporting.

Motivation

  • No existing index ranks U.S. water utilities by environmental health performance.
  • Infrastructure challenges include underfunding, aging pipes, cybersecurity threats, and increasing violations.
  • The index supports transparency, prioritization for funding, and accountability in public water infrastructure.

WCI Structure

WCI = Average of:

  1. Environmental Compliance (EC):

    • Health-based violations (40%)
    • Serious violator trends (40%)
    • Violations per site visit (20%)

  2. Truthful Reporting (TR):

    • Public notice + monitoring violations (40%)
    • Enforcement-to-violation ratio (60%)

Normalization: Min-max method used to scale inputs.

Data Sources

  • EPA ECHO / SDWIS datasets (2011–2020)
  • Filtered to large & very large PWS (serving >10,000 people)
  • Excludes: Small systems, Tribal systems, Territories
  • Population data: U.S. Census Bureau estimates

Methodology

  • Indicators derived from violations, enforcements, and compliance trends.
  • Weighted arithmetic calculations yield EC and TR scores per state.
  • Combined into a 0–1 WCI score, where lower = better.

Results

Top-performing states (lowest WCI scores):

Rank State
1 Indiana --> (0.03)
2 North Dakota
3 Minnesota
4 South Dakota
5 Michigan

Lowest-performing states (highest WCI scores):

Rank State
46 Arizona
47 Texas
48 California
49 Mississippi
50 Idaho --> (0.86)

Top EPA Region: Region 5 (Midwest)

Worst EPA Region: Region 10 (Northwest)

Sensitivity Analyses

  • SA-1: Reweighted EC to focus on health violations → minor rank shifts.
  • SA-2: Reweighted TR to focus on public health violations → larger shifts for lower-ranking states.
  • SA-3: Equal weighting of all inputs → stable top/bottom rankings; mid-range states more sensitive.

Limitations & Future Directions

  • Does not include small PWS or private wells.
  • TR score may overemphasize certain violations due to uneven frequency.
  • No economic or health outcome data included yet (e.g., cost of repair, hospital visits).
  • Future enhancements:
    • Add third component for public notification.
    • Link violations to health impacts or cost estimates.
    • Visualize results by EPA Region for policy impact.

Conclusion

  • The WCI provides a transparent, data-driven ranking of public water utilities based on SDWA compliance.
  • It can inform public awareness, EPA oversight, and infrastructure funding allocation.
  • It highlights the power of composite indicators in environmental decision-making.

Full report available here.