About the Water Treatment Plant

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​​​​​​Ann Arbor Water Logo

​​​​ 919 Sunset Road, Ann Arbor, MI 48103

8 a.m.-5 p.m.
(excluding holidays)

24/7 water emergency line



Molly Maciejewski,
Water Treatment Services Manager


1938.jpgThe Water Treatment Plant is actually two separate water plants.  The older plant was built in 1938 and 1949 and can process 22 million gallons of water per day (MGD).  The newer plant was built in 1966 and 1975 and can process 28 MGD.  The plants are upgraded continually to keep up with regulations, increase reliability and to improve water quality.

Water from both sources (the Huron River water and groundwater from local wells) is blended at the Water Treatment Plant and then moved through a rigorous treatment process. Because Ann Arbor uses surface water as a source for drinking water, we practice complete treatment which consists of:

  1. Rapid Mixing: for quick dispersion of the chemicals being added
  2. Flocculation (slow mixing): gives the chemical reaction the time it needs to go to completion
  3. Settling: the removal of solids from the water by gravity
  4. Filtration: to clean the water of physical, chemical and biological impurities
Because of the high level of hardness in Ann Arbor’s water supplies, Ann Arbor softens its water; lime softening uses calcium hydroxide to remove calcium, magnesium and iron. ​Lowering water hardness reduces build up and scaling on pipes, a factor that could extend the life of home hot water heaters, household pipes and other water-using appliances. Lower water hardness also reduces the amount of soap needed for effective cleaning and the potential for less spots remaining on utensils, glassware and dishware.

After softening the water is filtered and disinfected. Also, fluoride is added for dental protection (as recommended by the American Dental Association) and phosphate is added to stabilize the water after the softening process. ​