E. Coil. coli comes from ...

E. Coil.

coli comes from human and animal waste. During rainfalls, snow melts, or other types of precipitation, E. coli may be washed into creeks, rivers, streams, lakes, or groundwater. When these waters are used as sources of drinking water and the water is not treated or inadequately treated, E. coli may end up in the drinking water.
Public water supplies are usually disinfected with chlorine, ozone, or some other process. Finding E. coli in a public water supply indicates that the disinfection process was not working, or that contact with the waste occurred after the water was treated.
Himanshu has given a very nice description about the treatment you should do for the contaiminated water.