What is Graywater?

“Graywater” refers to wastewater generated from bathtubs, showers, bathroom sinks, laundry sinks and most clothes-washing machines. It does not include water from kitchen sinks, dishwashers or toilets.

In Longmont, wastewater enters household drains, moves through an interconnected system of sewer pipes and arrives at the wastewater treatment plant. There it undergoes treatment before being returned St. Vrain Creek for downstream uses.

Graywater reuse involves diverting home/building wastewater (specifically the type of wastewater mentioned above) before it heads to the sewer, providing basic treatment, and then putting the graywater to limited use. This could include flushing toilets or irrigating plants through subsurface systems. With minimal treatment, graywater is safe for these two purposes but cannot be used for drinking, recreation, surface irrigation, cleaning, or watering certain food crops.

Graywater in Longmont

A new state law, House Bill 24-1362, effective January 1, 2026, creates a statewide authorization of the installation of graywater treatment works and the use of graywater. The Act allows local governments to adopt an ordinance to prohibit the installation of graywater treatment works within its jurisdiction; otherwise, it will automatically become permissible in new construction.

Longmont does not currently permit the installation of graywater systems. While the city strongly supports water conservation and continues to expand related programs and outreach, permitting graywater reuse would require a specialized local oversight program to handle design reviews, inspections, enforcement, recordkeeping, and complaint resolution.

Longmont currently lacks the regulatory framework, staffing resources, and additional information necessary to implement and manage such systems safely and effectively. In November 2025, City Council passed Ordinance O-2025-73 prohibiting the installation of graywater systems in Longmont, consistent with existing rules and regulations. This decision does not close the door on future adoption.

Looking Ahead

Interest in graywater is increasing across Colorado, and Longmont will continue to evaluate whether developing a local control program makes sense. Factors the city will continue to monitor include:

• Technological improvements that could make graywater systems easier and more cost-effective to maintain
• Staffing and financial resources needed to administer a program
• Longmont’s unique water-rights considerations
• Community feedback and interest
• Potential water-saving benefits compared with other conservation strategies