Water Treatment Process

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To ensure that your drinking water is always safe, a process is used to treat millions of gallons of raw water that arrive daily at the three water treatment facilities serving Mesa. 

The City and its water treatment plants must meet rigorous standards established by the Environmental Protection Agency and the Arizona Department of Environmental Quality (ADEQ). The Brown Road Water Treatment Plant is capable of processing 72 million gallons per day and the Signal Butte Water Treatment Plant is capable of processing 24 million gallons per day. Both facilities are operated by ADEQ-certified operators. The raw water that feeds into the plants comes from the Central Arizona Project. The City also gets a portion of its drinking water from the Val Vista Water Treatment Plant, which is owned jointly by the cities of Phoenix and Mesa. Salt River Project supplies the raw water to the Val Vista Plant.

Raw water is processed as shown in the diagram below. The Signal Butte Water Treatment Plant also uses state-of-the-art ozone disinfection in the process.


Taste and Odor Removal

Taste and odors occur in the water in the late summer or fall.  Naturally occurring organic matter decomposes in the raw water source, and causes taste and odors.  Carbon or potassium permanganate is added to the water to remove or reduce unpleasant taste and odor.


As the water enters the treatment plant, chlorine dioxide is added for disinfection.  Disinfection destroys bacteria and viruses. Chlorine is added to the water as it leaves the treatment plant to ensure that the water that enters your home is safe to drink.


Aluminum sulfate (alum) is mixed into the water.  The alum causes small impurities to stick together and form "floc".


The floc settles to the bottom of the basin, and is removed.  Chlorine is also added during this process for further disinfection.


Water flows through filters that are made of layers of sand and coal.  These filters remove the fine particles that did not settle out during sedimentation.

Final Backwash

To remove particles from the filters, the filters are backwashed to remove sediment every 60 - 72 hours.  Approximately 200,000 gallons of water is used to backwash a filter.  This water is then recycled back into the raw water supply.


The raw water has naturally occurring fluoride, however, the Center for Disease Control (CDC) recommends an optimum fluoride level.  This requires the city to add supplement fluoride.


Water is stored in reservoirs throughout the City.  The distribution system brings the water to consumers.