The new Coliform Rule (June 29, 1989) ushered in a new era in coliform compliance requirements for drinking water. The new Coliform Rule sets the maximum contaminant level goal (MCLG) for coliforms at 0 per 100 ml and adopts a frequency-of-occurrence concept for compliance monitoring. The presence-absence (PA) approach establishes a coliform compliance limit based on the fraction of samples that contain coliforms during a given time period, in contrast to the old rule in which compliance was based on the arithmetic average of coliforms detected in water by the membrane filter (MF) method or the percentage of positive fermentation tube (FT) tests found over a 30 day period. The paper discusses the P-A concept as applied to coliform compliance monitoring. The newest approved method for total coliform testing, the minimal medium ONPG-MUG (MMO-MUG) test, is also discussed. Although the adoption of the P-A concept simplifies coliform reporting, the P-A test may be a more sensitive test than either the standard MF or FT test for coliform detection. This factor and the sampling requirements for coliform monitoring may force utilities to be more aggressive in evaluating preventative maintenance procedures, monitoring the function of filter beds and other treatment processes, and modifying distribution system management to assist in meeting the new coliform rule compliance requirements.