Day County, South Dakota
8 ZIP codes · Avg score 59/100 · Grade C · Updated 2026-06-04
Day County shows moderate water quality across its 8 ZIP codes — some areas carry violations worth monitoring.
How Day County Compares
How Day County Compares
Day County scores 1 points below the South Dakota state average (60/100) and 9 points below the national average (68/100).
Data: EPA SDWIS Last verified: 2026-06-04
ZIP Code Risk Map
Water Quality Map: Day County, South Dakota
Each dot represents a ZIP code. Color indicates water quality grade. Tap a dot for details.
Key Risk Factors
Health risk index: 14.8 (asthma 10.3%, diabetes 14.5%)
Estimated additional annual cost per homeowner: $1,056, driven primarily by flood
Infrastructure: 0.424% avg pipe failure probability, 75% of ZIPs at high risk
78.4% of homes built before 1978 (lead paint era)
County Health Indicators vs National Average
Black markers indicate national averages. Source: CDC PLACES, Census ACS.
Infrastructure Overview
Sources: Census ACS (housing age), EPA SDWIS (infrastructure risk model), state bridge inspection data.
Compound Risk Breakdown
Estimated additional annual cost per homeowner: $1,056
Bar widths proportional to share of total annual risk cost. Source: compound risk model (FEMA, EPA, USGS).
Housing Age Distribution
3,487 housing units in Day County
Source: U.S. Census Bureau ACS B25034 (Year Structure Built).
Water Safety Affordability
How much it costs to fix water issues relative to home values in Day County
Remediation costs are relatively manageable for most homeowners in Day County, representing a small fraction of property value.
Remediation includes water filtration, lead abatement, radon mitigation, and flood protection where applicable. Source: Census ACS, EPA SDWIS.
Health Outcomes vs National Average
CDC PLACES data for Day County residents
Black markers = national averages. Red = above national avg. Green = below. Source: CDC PLACES, Census ACS.
Water Systems with Most Violations
Top 5 systems in Day County ranked by EPA violation count.
| # | Water System | Population | Violations |
|---|---|---|---|
| 1 | Web Water Development Association | 20,750 | 4 |
| 2 | BROWN-DAY-MARSHALL RWS | 5,673 | 2 |
| 3 | Bristol | 288 | 2 |
| 4 | Grenville | 48 | 1 |
| 5 | PIERPONT | 129 | 1 |
10 total water systems serve Day County.
All ZIP Codes in Day County
8 ZIP codes tracked in Day County.
| # | ZIP Code | City | Safety Score | Grade | Violations | Home Value |
|---|---|---|---|---|---|---|
| 1 | 57261 | Roslyn | 70 | B | 0 | $114K |
| 2 | 57239 | Grenville | 68 | C | 1 | $291K |
| 3 | 57468 | Pierpont | 66 | C | 1 | $104K |
| 4 | 57219 | Bristol | 65 | C | 2 (1 health) | $83K |
| 5 | 57274 | Webster | 65 | C | 0 | $162K |
| 6 | 57273 | Waubay | 55 | C | 0 | $156K |
| 7 | 57256 | Ortley | 40 | D | 0 | — |
| 8 | 57422 | Andover | 40 | D | 0 | $95K |
Recommended Buyer Guides for Day County
Filtered against federal data, fitted to local risks.
- Best Lead Paint Test Kits — 78.4% of homes built before 1978
- Best Radon Test Kits — EPA Radon Zone 1 (highest risk) dominant in county
- Best Sump Pumps — Flood is the top compound risk factor
- Best Mold Test Kits — Flood-driven moisture and mold risk
Deep Dive Reports
Detailed analysis for Day County, South Dakota
Overview
Day County in South Dakota covers 8 ZIP codes with an average Home Safety Score of C (59/100).
3 of 8 ZIP codes have recorded EPA violations. 1 health-based violation have been documented.
← Back to South Dakota water quality report
Data Sources
- Water quality: EPA Safe Drinking Water Information System (SDWIS)
- Home values: U.S. Census Bureau ACS (median estimates by ZCTA)
Updated daily.