AWWA JAW28428

The Illinois Environmental Protection Agency is responsible for drinking water analyses for approximately 2,200 public water utilities serving more than half the state's population. The recently developed defined-substrate technology (DST, commercially known as Colilert), which simultaneously enumerates both total coliforms and Escherichia coli and does not require confirmatory tests, was compared in this geographic area with the membrane filter (MF) procedure from Standard Methods. Overall, there were no differences between MF and DST. Subcultures of positive DST tubes demonstrated this technology's specificity. Yellow (total coliform-positive) tubes yielded species consistent with total coliforms, and fluorescent (E. coli-positive) tubes contained E. coli. The DST system was easy to use and is compatible with new drinking water regulations that will increase monitoring and resampling requirements, mandate a fecal indicator (either an E. coli or fecal coliform analysis), and use a maximum contaminant level in the frequency-of-occurrence mode. DST also has several important advantages for state regulators, including its ability to help utilities comply with new transportation and storage requirements. Includes 23 references, tables, figure.