Water

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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, which is delivered directly into ponds via ditches, thereby saving on the costs associated with chemical and energy treatment of water.

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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 its customers with a reliable and adequate water supply. 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 and accounting, farm management, and conservation.

Colorado follows the Prior Appropriation Doctrine, also called 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.

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Colorado’s most senior water rights date back to the mid-1800s, when settlers dug ditches to mine for minerals and irrigate their 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. 

Citizen’s Guide to Colorado’s Water Heritage brings together the expertise of six prominent historians and scholars from throughout Colorado and the West to explore how water has shaped Colorado’s culture, history, and identity through the influences of Native Americans, Hispanos, and Anglo-Americans.

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The Water Court emerged to maintain civil order and established the Prior Appropriation Doctrine, preserving 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 the Water Court, ensuring the development and protection of Thornton’s water rights portfolio. View the Colorado Water Law Fact Sheet.