Groundwater was treated with chlorine and chloramine to study the incorporation and survival of Escherichia coli in developing biofllms in laboratory-scale units. Membrane filter and standard spread plate procedure were used to enumerate coliform and heterotrophic plate count bacteria respectively. Within 96 h the adhesion of heterotrophic plate count bacteria on stainless steel coupons was obvious in all systems, with a higher number of organisms (4 log cfu cm sq) noted for the non-disinfected water. Attachment of E. coli added 24 h after the formation of young biofllms was obvious on stainless steel coupons exposed to the non-disinfected water (9 cfu cm sq) and chlorinated water (2 cfu cm sq). A significant difference between E. coli counts in the non-disinfected water and chloraminated water, and the chlorinated and chloraminated water, was found. However, the ANOVA test indicated no significant difference in E. coli counts for the non-disinfected water and chlorinated water. This investigation revealed the effectiveness of chloramine in preventing the attachment of E. coli in developing biofilm.