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:
- Rapid Mixing: for quick dispersion of the chemicals being added
- Flocculation (slow mixing): gives the chemical reaction the time it needs to go to completion
- Settling: the removal of solids from the water by gravity
- 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.
Disinfectant Details
Ann Arbor’s Water Treatment Plant uses ozone as the primary disinfectant and chloramines as a secondary disinfectant. Chloramines or “combined chlorine” is a compound made up of chlorine and ammonia. These disinfectants are used as an alternative to chlorine treatment because they have fewer by-products, and are a longer lasting disinfectant than free chlorine. In addition, chloramines have less taste and odor than chlorine, and ozone is odorless. Ozone disinfection kills pathogens, improves water taste and reduces odors commonly detected in tap water.
