Tapped: The Denver metro region sits at the center of one of the American West’s most complex and consequential water challenges. This series examines the interconnected systems that determine how the region secures, stores, and conserves its water while navigating the competing demands of fast‑growing urban communities and the increasingly unpredictable mountain snowpack that underpins the entire system.

As the seat of the county, Castle Rock Water serves approximately 90,000 residents and the population is expected to nearly double by 2050.  While demand continues to grow, the water provider is working to reduce per‑capita use and transition away from a system that still relies heavily on nonrenewable groundwater aquifers.

Currently, only about one‑third of the water used in Castle Rock comes from renewable sources, and the town consumes more than 3.2 billion gallons of water annually. Much of that supply is drawn from the Denver Basin aquifers, a resource water officials say must be protected for long‑term reliability.

“I think that Denver basin groundwater is a great resource that needs to be protected for the long term so that it will be available for drought years,” Castle Rock Water Director Mark Marlowe said. “Douglas County water providers, including Castle Rock, need to be developing renewable water supplies to complement that non-renewable groundwater so that we can protect that resource.”

While renewable supplies are subject to weather variability, Castle Rock’s deep groundwater resources provide a level of drought resilience.

“Castle Rock’s in a very good position because we do have this Denver Basin and deep groundwater supply. What that does is that supply is generally much less impacted by drought from a supply standpoint,” Marlowe said. “The important thing is to make sure when we do get a lot of rain and snow that we’re capturing that water and eventually putting some of that excess supply back to that Denver Basin groundwater.”

CRW aims to meet 100% of future demand with renewable supplies in an average year by 2065, using groundwater primarily during droughts. A key part of that strategy involves aquifer recharge and storage, which allows the town to inject renewable surface water back into the Denver Basin when conditions permit.

“One of the great things about our Denver Basin aquifers is we’re doing aquifer recharge and storage,” Marlowe said. “As we develop renewable surface water supplies, we actually put water back into the deep Denver Basin groundwater.”

To build out renewable capacity, Castle Rock Water has invested heavily in infrastructure, storage and regional partnerships. The water authority is currently expanding the Plum Creek Water Purification Facility, doubling production capacity from six million gallons per day to 12 million gallons per day. The district has also completed two new reservoirs that will help store water collected during wetter periods for later use.

Marlowe said those projects are necessary but costly.

“All of the renewable water supplies require large investments in infrastructure,” Marlowe said. “The cost of the Plum Creek expansion is about $75 million … and the reservoirs, which provide roughly one tenth of the total annual needs, about $28 million.”

Additionally, Castle Rock Water has invested about $29 million in land and water rights in Weld County. The project is expected to secure 2,500 acre-feet and is anticipated to be completed around 2030.

CRW also receives supplies through regional partnerships including the WISE program, participates in the Platte Valley Water Partnership and makes use of legally reusable water. Reuse, Marlowe said, is expected to become an increasingly important component of the town’s long‑term water portfolio.

“Reuse is a huge part of our system. Roughly 33% of our water supplies, long term, will be reusable,” he said.

Alongside supply side investments, Marlowe said that conservation efforts can have a significant effect, stretching existing resources.

“We’re looking at trying to reduce our per capita use by about 20% between now and 2050,” Marlowe said.

The town has eliminated turf grass in the front yards of new developments and instead requires low‑water landscaping. CRW also offers several rebate programs aimed at reducing outdoor water use and improving efficiency, including one of the highest turf replacement incentives in Colorado at $3.25 per square foot for replacing high‑water‑use lawns with drought‑tolerant landscaping. 

As development continues, builders pay about $44,000 per home in system development fees to connect to Castle Rock Water’s infrastructure, helping fund long‑term investments.

“We’re doing really well in terms of that and making a ton of progress and I think where we’re really headed is to a much more reliable system, long term,” Marlowe said.

Looking ahead, Marlowe said the utility plans for a wide range of growth scenarios as it evaluates whether future water supplies will meet demand.

“Castle Rock Water is really planning for both current residents and projected population growth,” Marlowe said.