The average raw water contamination with which a water treatment process employing chlorination alone can usually produce a water meeting the Treasury Department Standard is generally 50 coliform organisms per 100 ml, provided a maximum pollution of 400 coliform organisms per 100 ml is not exceeded more than 5 percent of the time. The percentage of coliform bacteria and the frequency of occurence of high degrees of pollution in Lake Michigan via the Calumet River and Saginaw Channel was requested to carry away an increasing amount of pollution entering the lake.