Castle Rock Water outlines regional plan to boost renewable supply, promote 'Colorado scape' and increase reuse

Castle Rock Water Director Mark Marlow told the Douglas County Water Commission that Castle Rock is pursuing a regional approach to reduce reliance on Denver Basin groundwater and increase renewable water supplies, using storage, reuse, aquifer storage and expanded partnerships with neighboring providers.

Marlow said Castle Rock Water already serves some unincorporated areas of Douglas County and is pursuing projects to connect more developments to renewable supplies. "All water is reused. We all know that," Marlow said, describing reuse as a core part of the utility’s supply strategy.

The utility is pursuing five main lines of work: regional partnerships to share infrastructure and costs (including participation in the WISE project and agreements with Parker Water and others); increasing storage capacity (including new and expanded reservoirs and ownership shares in Reuter‑Hess and Chatfield storage); aquifer storage and recovery (ASR) using municipal wells; expanding water purification/reuse capacity at the Plum Creek Water Purification Facility; and demand reduction through conservation and landscaping regulations.

Marlow provided several program details during the presentation. Castle Rock has taken service for Bell Mountain Ranch and provides water/wastewater service to the Macanta development; the utility is building new tanks and pump stations and has redrilled wells and upgraded treatment at acquired systems. The Plum Creek purification facility is being expanded from 6 million gallons per day to 12 million gallons per day; Marlow described the expansion as a near‑term driver of renewable supply and said the project carries an approximate $75,000,000 price tag. He also said the utility has invested about $270,000,000 to date in long‑term renewable supply and has nearly $500,000,000 planned through 2065.

On reuse and direct potable reuse (DPR), Marlow said Castle Rock favors reuse (indirect reuse is already used) and is studying DPR but is constrained by regulatory and permitting costs. He said the utility would prefer DPR permits that could be activated in drought emergencies rather than carrying full DPR permitting costs at all times. Marlow said the town aims for reuse to represent about one‑third of its supply where feasible.

Marlow described current operational numbers and targets: the system serves roughly 90,000 people; systemwide usage averaged about 112 gallons per capita per day when commercial uses are included, while individual residential customers average near 100 gallons per capita per day; and summer peak days can reach 20 million gallons while winter use is typically 5–7 million gallons per day. He said reducing nonfunctional turf through the town’s "Colorado scape" landscaping rules and rebates (about $3.25 per square foot) is central to lowering peak demand and long‑term capital costs. "If we can get to 100 gallons per day per capita, overall for our system, we can save on the order of 70 or more million dollars in capital expense for our customers in the long term," Marlow said.

Marlow described several supply sources: a WISE allocation (he said Castle Rock currently holds about 2,000 acre‑feet of a 10,000 acre‑foot WISE pool), about 2,500 acre‑feet in the Box Elder/Lost Creek basins in Weld County (subject to water‑court processes), and local rights on Plum Creek, Cherry Creek and the South Platte. He also discussed partnerships and projects that move or treat water, including agreements to own or use storage at Reuter‑Hess and Chatfield reservoirs and a first public‑private infrastructure phase in Weld County with Tallgrass (a private partner). He noted the Denver Basin groundwater supply will remain an important drought‑resistant source but that its use should be managed over time.

Marlow described ASR activity, noting roughly four to five wells had been used recently to store renewable water back into the aquifer and that Castle Rock is exploring broader regional ASR efforts. He invited commissioners to tour ASR sites, saying the facilities are mostly below ground but that staff would show wells and explain operation on a tour.

Commission members asked operational and policy questions. Clark Hamilton, a commissioner and Castle Rock resident, described converting his own yard from turf to Colorado scape and said: "I went from 8 zones...down to 2 drip line zones now. I'll see about 3 quarters of my outdoor water usage disappear." Commissioners and staff discussed the difficulty small special districts face in meeting regulatory and capital requirements; Marlow said it is often cheaper and more feasible for larger providers to acquire or serve small systems and described Castle Rock’s recent takeover and rehabilitation of Bell Mountain Ranch as an example.

Marlow and commissioners also discussed regulatory details for reuse and DPR—testing requirements, pretreatment programs for industrial contributors to wastewater, and the incremental regulatory costs that come with a full DPR permit. He said those costs are a major factor in deciding whether to pursue full DPR now or reserve it for drought emergencies.

Administrative items tied to the meeting: the commission approved minutes from the prior meeting; Roger Hudson moved to accept the minutes and Clark Hamilton seconded. The commission also asked staff to follow up with water providers that have been slow to respond with data for the county’s supply/demand study and to coordinate updates. Lauren Pulver (staff) reported the county had received responses from seven of the 34 providers asked for data (Aurora, Castle Pines Metro, Castleton Water and Sanitation District, Larkspur, Littleton, Sedalia, and Sierra Vista Douglas Mutual Water Company).

Next steps and scheduling: commissioners said they will continue to invite major in‑county providers for presentations; Parker Water and Highlands Ranch Water were discussed as likely future presenters. Staff said a public outreach open house tied to the county water study will likely be delayed until after a June special election and is now expected in late summer or early fall; Forest Green (the county’s consultant) will return in June to present a public engagement plan and stakeholder list.