Arapahoe County Water Report

Arapahoe County earns an A grade for drinking water quality, scoring 69.8 out of 100. Over the past five years, EPA SDWIS records 9 health-based violations — a pattern that public water utilities are required to disclose and correct.

Under the Clean Water Act §303(d), EPA ATTAINS tracks whether waterways meet quality standards for drinking, recreation, and aquatic life (reporting cycle: 2022). A substantial 38.9% of assessed waterways are impaired (91 of 234 water bodies) across Arapahoe County's watersheds. The leading impairment causes are escherichia coli (e. coli) and arsenic. Impairment does not mean tap water is unsafe — it measures ambient waterway conditions upstream of treatment, not finished drinking water.

USGS NWIS gauge data (as of 2026-05-14T13:00:00.000-06:00) puts SOUTH PLATTE RIVER at 28.4 cfs — well below its long-term average at 12% of mean — low-flow conditions worth noting for water-dependent ecosystems. Streamflow is a leading indicator of drought stress, sediment load, and dilution capacity: low flows concentrate pollutants and warm water temperatures, stressing aquatic life and, in surface-water-dependent systems, the source water quality for treatment plants.

EPA's Water Quality Portal (WQP) aggregates monitoring data from federal, state, and tribal agencies. Arapahoe County has extensive coverage with 58 active monitoring sites with 16,368 recent measurements on record. Predominant monitoring categories include nutrient and physical. More monitoring sites generally indicate greater scientific attention to local water conditions — and provide the baseline data that regulators use to set future impairment listings.