Douglas County is trying to outrun its own growth, hustling to move off decades of groundwater dependence just as its population edges toward 400,000. Water managers in Highlands Ranch, Parker and Castle Rock say the Denver Basin aquifer that helped fuel the suburban boom cannot carry the county forever, so districts are pouring money into treatment plants, storage and pipeline projects to pull more renewable surface water into the mix. At the center of those plans sits the 75,000 acre-foot Rueter-Hess Reservoir, which officials now treat as the county’s main hub for capturing water in wet years and saving it for the dry ones.
The urgency shows up in the planning documents and public briefings. The three largest providers – Highlands Ranch Water, Parker Water & Sanitation District and Castle Rock Water – supply roughly two thirds of Douglas County’s municipal demand, and Parker still serves about 78,000 residents while shifting from roughly 90% groundwater in the early 2000s to about 60% groundwater today, officials told the Denver Gazette. Managers say that change comes from a mix of conservation and construction, as reuse, imported supplies and new treatment capacity are layered into the system. The county’s patchwork of 31 providers can make coordination messy, but it also gives officials multiple levers to pull, including storage, treatment and legal water rights.
Platte Valley Pipeline and New Storage
The biggest engineering gamble on the table is the Platte Valley Water Partnership. The proposal would capture South Platte River flows in northeastern Colorado and send them back to Rueter-Hess through new reservoirs and a roughly 125 mile pipeline, with an estimated price tag near 780 million dollars, according to the project description from the Parker Water & Sanitation District. Supporters say the project is designed to snag excess spring runoff in wet years, store it and reuse it, so districts do not have to burn through nonrenewable aquifers every time the region hits a dry spell.
Castle Rock Doubles Down on Treatment and Water Rights
Castle Rock is betting heavily on treatment upgrades and long term water rights. The town is expanding its Plum Creek Water Purification Facility from 6 million gallons per day to 12 million gallons per day so it can handle reuse and imported supplies, and it has been buying land and South Platte water rights to lock in more renewable sources. As outlined by the Town of Castle Rock, the utility has invested about 29 million dollars in Weld County water rights since 2021 and is aiming to push its renewable share significantly higher over the coming decades.
Highlands Ranch Leans on Reuse and Aquifer Recharge
Highlands Ranch Water is trying to stretch what it already has. The district reports that it has injected more than 15,000 acre-feet of water into about 25 wells and captures roughly half of its surface water supply for reuse, which helps cut net withdrawals from the groundwater system, according to Highlands Ranch Water. Managers also point to long running demand management programs, including water budgets, turf replacement rebates and smart irrigation incentives, that have helped hold per capita use in check even as the local population climbed.
What It Means for Residents
The recipe now in play – build, buy and conserve – comes with both a calendar and a price. U.S. Census estimates put Douglas County at about 394,000 residents in 2024 and near 399,400 by mid 2025, and utilities are already warning that modest rate adjustments will be part of paying for long term pipelines and treatment upgrades, according to local reporting and public notices. Planners keep emphasizing the pairing of conservation with infrastructure so that customer impacts are spread out while the region moves away from nonrenewable groundwater…