Water Sources & Treatment

IN THE WORKS: In 2025, we began work to install new filters to our CPNMD treatment plant. This is the last of many upgrades to improve performance and increase capacity by 2 million gallons total to meet growing demand. More information is available on the project page. Read about treatment plant upgrades here. 

Graphic detailing key numbers about the District’s water system, including: 2 primary water sources – well/groundwater in summer and renewable water through Highlands Ranch Water in winter; up to 4.5 million gallons treated daily at CPNMD’s treatment plant in summer and an average of 700,000 gallons in winter; 24/7 water quality monitoring and 240+ water samples taken per year to ensure water meets state/federal regulations; 3.75 million gallons stored in 3 treated water tanks; 71 miles of water pipeline to deliver water to customers; and 80% of treated water used for outdoor irrigation.

Our Water Sources & Infrastructure

CPNMD water comes from two primary sources, based on the time of year:

May through September – Well/Groundwater: During the majority of summer,  local water wells draw from the Arapahoe, Denver, and Lower Dawson Aquifers. These sources are the result of water rights that date back to the formation of the District. Water is treated at our water treatment facility, moved ro storage tanks, and supplied to customers on demand. Each fall, our operations team shuts down our Water Treatment Plant and activates our interconnect with Highlands Ranch Water.  

October through April – Renewable/Surface Water: We take full advantage of our renewable water resources through an agreement with Highlands Ranch Water. In 2010, the District purchased Hock Hocking (Park County) and Upper Platte River rights to include surface water in our asset portfolio. This water is stored in Chatfield Reservoir, where CPNMD owns and has access to 1,006 acre-feet of storage capacity.

During fall and winter, Highlands Ranch Water treats our renewable water. It is pumped through our distribution system that primarily serves serves CPNMD, the Town of Castle Rock, and Castle Pines Metropolitan District. Treated wastewater return flows are captured and used as the primary source of irrigation water for The Ridge Golf Course.

Treating Our Water

In May through September, CPNMD water is treated by our treatment plant. From October to April, Highlands Ranch Water treats our renewable water, which is then pumped through our interconnect pump station and pipeline into our water distribution system.

This annual switch in water sources helps extend our non-renewable water supply and allows us to complete project work and perform maintenance at the treatment plant.

There are slight aesthetic differences in the two water source that some residents may notice:

  • HARDNESS: Our renewable water (October through April) is much harder than the supply in our deep well aquifers. Residents may notice nuances like water spots on dishes or fixtures.
  • TASTE: Some residents report that they notice a shift in the taste of our renewable water (October through April). It is often described as "earthy, or metallic." The water is absolutely safe to drink and for all other uses. Highlands Ranch Water has made improvement at its treatment plant to help combat this aesthetic issue, and we anticipate that these differences will be less noticeable iin the time to come. 

For more information on these sources, review our Water Quality Report.