Water

Water Sources
The vast majority of Cincinnati is served by the Greater Cincinnati Water Works. GCWW has two plants that supply the area. The Miller Treatment Plant treats surface water from the Ohio River and supplies 88% of drinking water to GCWW's customers, including most of the City of Cincinnati. The Bolton Treatment Plant treats groundwater from ten wells in the Great Miami Aquifer. It is located in southern Butler County. Our aquifer (buried sand and gravel filled with water) is 150-200 feet deep and two miles wide. Bolton Plant supplies about 12% of GCWW water.

To see which water source you are served from see the map here: http://www.cincinnati-oh.gov/water/pages/-3031-/

So, in the city, we are served by the Miller Plant. This means our water is collected from the Ohio River. The Ohio River Watershed is very large ( here is a map: http://www.orsanco.org/rivinfo/basin/basin.asp ). Water in Cincinnati could presumably have started in any area more or less upstream of the city in that basin. After is is collected, it goes through a treatment process (detailed here: http://www.cincinnati-oh.gov/water/pages/-3283-/ ) and then is pumped to homes and businesses. A map of the GCWW's plants can be found at: http://maps.google.com/maps/ms?msa=0&msid=113527232130502588508.000452b133642147a42df

Watershed
The Ohio River Watershed is very large ( here is a map: http://www.orsanco.org/rivinfo/basin/basin.asp ). It looks like you'd have to drive to the upper portion of Ohio (Lima, Findlay, or Akron maybe) to get out of this watershed. Probably near 200 miles at the closest.

Rainfall
The total rainfall in 2007 was 36.72 inches. Source: http://news.cincinnati.com/apps/pbcs.dll/article?AID=/20080805/NEWS01/808050319