Thornton
Thornton, CO water profile — supply sources, drought status, wastewater reuse, and the key water issues facing the city.
thornton city of
surface water (rivers/reservoirs) · local government · PWSID CO0101150
Below EPA's 15 ppb lead action level at last testing.
Source: EPA Safe Drinking Water Information System (SDWIS) · 2026 Q1
Thornton, CO is a mid-sized city, with a population near 133,451 and the 6th-largest community in Colorado. Like much of Colorado, Thornton draws its water primarily from Colorado River headwaters, South Platte, Arkansas River, and snowpack.
Thornton's water outlook is shaped most by colorado river — the issue that dominates planning across Colorado. As the headwaters of the Colorado River, Colorado faces both upstream obligations and rapid Front Range growth; the state approved direct potable reuse regulations in 2022.
Thornton sits in a state that reuses roughly 14% of treated wastewater (developing programs) and currently experiences exceptional drought.
For the bigger picture, see the Colorado state water profile and the related issues below.
Adams County water quality
Source: EPA SDWIS · 2026 Q1
At a glance
- Population ~133,451 (6th-largest in Colorado)
- Primary sources: Colorado River headwaters, South Platte, Arkansas River, and snowpack
- Drought: exceptional conditions
- State reuse rate: ~14% of wastewater
Statewide drought history
% of Colorado in severe+ drought (Exceptional (D4) now).
Source: U.S. Drought Monitor
Common questions
Is tap water safe in Thornton?
Thornton's largest water system, THORNTON CITY OF, serves about 226,465 people. EPA records show 0 health-based violation(s) since 2016 and a most-recent 90th-percentile lead level of 2.3 ppb (EPA action level is 15 ppb). Always check your own provider's annual Consumer Confidence Report.
Where does Thornton get its water?
THORNTON CITY OF draws primarily from surface water (rivers/reservoirs), part of Colorado's supply from Colorado River headwaters, South Platte, Arkansas River.
Related water issues
Colorado River
The river that supplies 40 million people has lost roughly a fifth of its flow since 2000, forcing a renegotiation of how seven states share the water.
ExploreDrought
Much of the American West is in a multi-decade dry period that researchers describe as the most severe in over a millennium, reshaping how communities plan for water.
ExplorePotable Reuse
Advanced purification turns treated wastewater into water that meets or exceeds drinking-water standards — increasingly essential in water-stressed regions.
ExploreAgricultural Demand
Agriculture accounts for the majority of consumptive water use in the West, making farm efficiency and water markets central to any supply solution.
Explore