When lead levels in drinking water are elevated, optimal corrosion control treatment (OCCT) is required by the Safe Drinking Water Act to install the best treatment to reduce lead at a customer's drinking water taps. The treatment is called optimal because it is the best method to reduce lead and will not cause the water system to violate any other part of the Colorado Primary Drinking Water Regulations.
There is a current stakeholder process regarding the OCCT designation for Denver Water, beginning in March 2018.
Phosphorus and drinking water systems
Phosphorus is a natural element commonly used by systems to provide corrosion control in their pipes to prevent lead from leaching into the water. This interactive map has two tabs, and will show you which the systems in Colorado use this treatment, and where they are located.