Weld County, Colorado: drinking water report. Weld County in northeastern Colorado has a population of about 330,000, including Greeley, Evans, and Windsor.
Weld County in northeastern Colorado has a population of about 330,000, including Greeley, Evans, and Windsor. The county is Colorado's agricultural heartland – the top-producing agricultural county in the state – and also one of the most active oil and gas producing counties in the country. Water comes from the Cache la Poudre River, the Colorado-Big Thompson Project, and groundwater wells, creating a three-way intersection of agriculture, energy extraction, and residential water demand.
The convergence of concentrated animal feeding operations (CAFOs), irrigated farmland, and over 20,000 active oil and gas wells creates a complex contamination landscape. According to the Colorado Oil and Gas Conservation Commission's 2024 data, Weld County has experienced 47 documented groundwater contamination incidents from oil and gas operations since 2010, including cases involving benzene, methane, and produced water.
Nitrate from agricultural operations is elevated in shallow aquifer zones across the county. A 2023 CDPHE assessment found that 15% of private wells tested in Weld County exceeded the nitrate MCL of 10 mg/L. The EPA's UCMR5 data shows PFAS detections in the Greeley system at low levels.
Weld County's combination of agriculture and oil and gas activity means private well owners face risks from both directions. Testing for nitrate, methane, and petroleum compounds provides a baseline that covers the most likely contaminants.
Check your water for current data on public systems. For nitrate, reverse osmosis is effective. For petroleum compounds, activated carbon filters help. Our water filter guide covers multi-contaminant scenarios. Pull your detailed report for trends, and visit our Colorado page for statewide patterns.