Castle Rock switches water disinfection to free chlorine Feb. 2 through May

Castle Rock Water will temporarily convert the town’s distribution system disinfection from chloramines (monochloramine) to free chlorine to perform system-wide flushing and cleaning, the town announced in a public notice. The maintenance is scheduled to begin Monday, Feb. 2, and the town expects the work to continue through May.

The town’s public notice and the town website describe the work as routine maintenance used by many water providers. Officials say free chlorine will be used during the maintenance period and the system will return to chloramine before irrigation season. The Colorado Department of Public Health and Environment must approve the flushing and sampling plan before conversion begins, and staff are finalizing that plan as part of operational preparations.

Officials warned customers the change may be noticeable. Mark Marlowe, speaking for Castle Rock Water, said: “The water is perfectly safe, and this is nothing to be concerned about, but people will notice a difference.” Town messaging adds that the maintenance is a standard procedure and that “throughout the maintenance period, free chlorine will be used in the system before transitioning back to chloramine.”

There is a minor discrepancy in reporting about the timing. Local coverage noted staff said the conversion could begin in January and described a 60-90 day window for the program. The town’s official notice, posted Jan. 28, specifies the Feb. 2 start date; both accounts, however, describe a multi-month temporary switch that aligns broadly with a return to chloramines before irrigation season.

Castle Rock staff briefed the Town Council on the plan and signaled outreach and customer service efforts are in place. The town will conduct targeted outreach to dialysis centers and other facilities that rely on treated water, and staff expect customer calls during the conversion. To handle inquiries, the town is preparing scripts and fact sheets for customer service personnel. Residents with questions can dial 720-896-TOWN (8696) to reach a menu for frequently asked questions or live assistance during business hours.

The switch is part of long-term system management. Castle Rock converted to chloramines in 2013, and officials said temporary conversions may be needed roughly every five to 10 years depending on system conditions such as temperature and water age in storage tanks.

For Douglas County residents, the practical impacts are sensory and informational: short-term differences in taste, odor or slight color in the first days of conversion and a possible increase in calls to utilities. The town has pledged regulatory oversight, public outreach and a return to chloramines before peak outdoor irrigation, so most customers should experience no interruption in safe drinking water.