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Water Treatment Process

Water Treatment Process

Big debris (sticks, plants and fish) are screened from the water prior to the water entering the treatment plant. After screening, water is piped to the water treatment plant.


Chlorine can be added at different locations in the treatment process to kill disease causing microorganisms and prevent microorganisms from growing during the water treatment process. This is usually done before filtration.


Coagulants are added to the water to aid in particulate removal. Aluminum sulfate is used as the coagulant at the Betasso Water Plant, while aluminum sulfate and a polymer are used at the Boulder Reservoir Treatment Plant. At the coagulant feed point, the water is mixed rapidly too distribute the chemicals evenly. The coagulant breaks down repelling forces between small suspended particles. This rapid mix is followed by a slow mix. During the slow mix, the suspended particles begin to form larger collections of solids called "floc." This process is called "flocculation."


Water then goes into four basins at Betasso where the larger, heavier, floc particles settle to the bottom. The Boulder Reservoir Treatment Plant uses Dissolved Air Flotation, or DAF units. DAF is a physical process where microbubbles attach themselves to particles in the water and float them to the surface where they form a removable, floating sludge blanket.


After the sedimentation process, the water flows to the filters where the smaller floc particles are filtered from the water.


After filtration, just enough chlorine is added to the water to keep the piping system and storage reservoirs in the City of Boulder free from pathogens and to maintain a residual to the tap as required by state law.

Corrosion Control

At the Betasso Water Treatment Plant, calcium hydroxide (lime) and carbon dioxide are added to the water after filtration to raise the alkalinity (buffering capacity) and pH of the water to make it less corrosive to pipes. At the Boulder Reservoir Water Treatment Plant, alkalinity and pH are consistent with Betasso's water.


Boulder began adding fluoride to its water supply following voter approval of a 1969 ballot measure. At both treatment plants, fluoride is added to the finished water for dental health.

On Feb. 22, 2016, the City of Boulder’s Utilities Division decreased the amount of fluoride added to the drinking water, from 0.9 to 0.7 mg/L based on updated federal and state guidance.

In 2015, the United States Department of Health and Human Services reduced the recommended fluoride level for oral health benefits to 0.7 mg/L in drinking water and issued revised guidance to water systems that add fluoride. The Colorado Department of Public Health and Environment has subsequently endorsed that guidance. Fluoride levels in the city’s drinking water will continue to remain below both maximum levels and maximum level goals established by the United States Environmental Protection Agency. 


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