standley lake

​Water Supply

Where Thornton’s Water Comes From

Thornton’s water supply comes from snowpack in the Rocky Mountains. Each spring, the snow in the South Platte River Basin begins to melt, and the water flows into Clear Creek and the South Platte River. Based on the priority of Thornton’s water rights, water is diverted into ditches and stored in our reservoirs. One of Thornton’s water treatment facilities treats and cleans the water, and drinking water is distributed to utility customers. Some of Thornton’s parks are irrigated using non-potable water, delivered directly by ditches into ponds, saving chemical and energy water treatment costs. 

Water Resources Division

Ditch headgate 

The City of Thornton Water Resources Division is charged with obtaining and protecting the city’s water rights to ensure an adequate water supply for all Thornton utility customers. Thornton’s diverse water portfolio, including senior rights dating back to the 1860s, provides an adequate and reliable water supply for its customers. Thornton currently manages water rights in the South Platte River, Clear Creek, and Cache la Poudre River basins. This division also monitors activities within these basins and their tributaries for impacts on Thornton’s water supply. The Water Resources Division performs these core water rights and supply functions - planning, development, protection, water supply maintenance, operations & accounting, farm management, and conservation.


One of the division’s responsibilities is to ​evaluate how much water the city will have in the event of a prolonged drought. When drought status changes, Water Resources staff follows the city’s Drought Management Plan to ensure delivery of an adequate water supply to all utility customers. Living in the semi-arid climate of Colorado means that water restrictions are a reality due to naturally occurring drought cycles. By conserving water year-round and using water wisely, you can help sustain our water supply. 

Water Rights and Water Law

historic photo of Croke Canal 

Historical Photo of Croke Canal Headgate

Colorado follows the Prior Appropriation Doctrine, also referred to as the “First in Time, First in Right” doctrine. Colorado’s water rights system sets the framework for distributing raw water when the supply in a stream is insufficient to meet everyone’s needs, which is often the case.

Colorado’s most senior water rights originated in the mid-1800s when settlers dug ditches to mine for minerals and irrigate farms. Over time it became apparent that there was not enough water for everyone, and the concept of “First in Time, First in Right” was born. Those who put the water to beneficial use first had the priority to use it. This process continued down the priority list, leaving some users high and dry. Water Court emerged to keep civil order and created the Prior Appropriation Doctrine, keeping the “First in Time, First in Right” concept intact. The Water Court ordered that all current and future water use be decreed. Thornton’s Water Resources Division plays an active role in Water Court, ensuring the development and protection of Thornton’s water rights portfolio.