Water Treatment Process
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 two 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), and must be
free of coliform bacteria. The Brown Road Water Treatment Plant
(BRWTP) is capable of processing 72 million gallons per day, and
the facility is operated by ADEQ-certified operators. The raw
water for the BRWTP 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 Val Vista.
The raw water is processed according to the following steps:
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.
Disinfection
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 insure that the water that enters your home is safe to
drink.
Flocculation
Aluminum sulfate (alum) is mixed into the
water. The alum causes small impurities to stick together and
form "floc".
Sedimentation
The floc settles to the bottom of
the basin, and is removed. Chlorine is also added during this
process for further disinfection.
Filtration
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.
Fluoridation
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.
Storage
Water is stored in reservoirs
throughout the City. The distribution system brings the water
to consumers.