State Well Water Guide
Colorado Private Well Water Guide
About 25% of Coloradans rely on private wells, primarily in rural agricultural communities on the Eastern Plains, mountain towns without public water systems, and exurban foothills communities. Colorado's varied geology creates distinct regional risks: naturally occurring arsenic and uranium in the Front Range's granitic and volcanic geology, nitrate from the Eastern Plains' agriculture and confined feeding operations, naturally elevated fluoride in some plains aquifer systems, and PFAS from military and industrial sources along the Front Range. CDPHE regulates well construction under the Colorado Water Well Construction Rules.
Testing Guidance
CDPHE recommends annual testing for coliform bacteria and nitrates for all private wells. Front Range and mountain well owners should test for arsenic and uranium. Eastern Plains well owners should prioritize nitrate testing. Wells near Buckley SFB, Peterson SFB, Schriever SFB, and Fort Carson should be tested for PFAS. Fluoride testing is recommended for deep aquifer wells on the Eastern Plains.
What to Test For in Colorado
Total coliform bacteria and E. coli — annual minimum
Arsenic — Front Range granitic and volcanic rock wells; Denver Basin formation wells
Nitrates — Eastern Plains agricultural areas and areas with septic density
Uranium — Front Range and mountain wells in uranium-bearing geology
PFAS — near Buckley SFB, Peterson SFB, Schriever SFB, Fort Carson, and the Colorado Springs military corridor
Fluoride — Eastern Plains deep aquifer wells (Laramie-Fox Hills, Denver aquifer systems)
Iron and manganese — Denver Basin bedrock aquifer wells
Radon — mountain and Front Range granite wells
Common Contamination Risks in Colorado
Arsenic from Front Range geology — granitic, volcanic, and sedimentary formations in the Denver Basin and mountains contain naturally elevated arsenic
PFAS from Colorado Springs military corridor — Buckley, Peterson, Schriever, and Fort Carson form one of the densest concentrations of military PFAS sources in the nation
Nitrate from Eastern Plains agriculture — cattle feedlots and row crops in the Eastern Plains contribute to aquifer nitrate loading
Uranium from igneous and sedimentary geology — Colorado has extensive uranium-bearing geology, and groundwater uranium can be elevated in both mountain and plains wells
Fluoride in deep plains aquifers — some Denver Basin deep aquifer systems have naturally elevated fluoride
Contaminant Guides Relevant to CO Wells
PFAS
Synthetic Chemicals
EPA limit: 4 ppt
Lead
Heavy Metals
EPA limit: 15 ppb (action level)
Nitrates
Agricultural Chemicals
EPA limit: 10 mg/L
DBPs
Disinfection Byproducts
EPA limit: 80 µg/L (TTHMs) / 60 µg/L (HAA5)
Arsenic
Heavy Metals
EPA limit: 10 ppb
Hard Water
Minerals
EPA limit: No federal limit
Chlorine
Disinfection Chemicals
EPA limit: 4 mg/L (MRDL)
Microplastics
Emerging Contaminants
EPA limit: No federal limit
Bacteria
Microbial Contamination
EPA limit: Zero E. coli / < 1 coliform per 100 mL
Fluoride
Minerals
EPA limit: 4 mg/L (MCL) / 2 mg/L (Secondary MCL)
Chromium-6
Heavy Metals
EPA limit: 100 ppb (total chromium)
Copper
Heavy Metals
EPA limit: 1.3 mg/L (action level)
Radon
Radioactive Contaminants
EPA limit: No finalized MCL
Iron & Manganese
Minerals
EPA limit: 0.3 mg/L iron / 0.05 mg/L manganese (aesthetic SMCLs)
Atrazine
Agricultural Chemicals
EPA limit: 3 ppb (0.003 mg/L)
Uranium
Radioactive Contaminants
EPA limit: 30 µg/L (30 ppb)
Perchlorate
Industrial Chemicals
EPA limit: 0.056 mg/L (56 ppb)
VOCs
Industrial Chemicals
EPA limit: Varies by compound: benzene 5 ppb; TCE 5 ppb; PCE 5 ppb; vinyl chloride 2 ppb
Radium
Radioactive Contaminants
EPA limit: 5 pCi/L (combined Ra-226 + Ra-228)
Crypto & Giardia
Microbial Contamination
EPA limit: Zero (treatment technique standard)
Hydrogen Sulfide
Naturally Occurring Compounds
EPA limit: No MCL; Secondary MCL (aesthetic) of 0.05 mg/L
Selenium
Minerals
EPA limit: 50 ppb (0.05 mg/L)
Cadmium
Heavy Metals
EPA limit: 5 ppb (0.005 mg/L)
Mercury
Heavy Metals
EPA limit: 2 ppb (0.002 mg/L)
Barium
Heavy Metals
EPA limit: 2 mg/L
Find a Certified Lab in Colorado
Use the Colorado state-certified laboratory program to find accredited labs for private well testing. Always verify current certification before submitting samples.
CO Certified Lab Directory ↗Colorado Well Water FAQs
Related Pages
Data Sources & Provenance
All data on this page is sourced from official U.S. government or public datasets.
Quick Reference
State program
CO Certified Labs ↗EPA guidance
EPA Private Wells Program ↗State lab directory
CO Certified Labs ↗Minimum Annual Tests
Plus state-specific contaminants listed above
Other State Guides