Method 1106.1 describes a membrane filter (MF) procedure for the detection and enumeration of the enterococci bacteria in ambient water. The enterococci bacteria are commonly found in the feces of humans and other warm-blooded animals. Although some strains are ubiquitous and not related to fecal pollution, the presence of enterococci in water is an indication of fecal pollution and the possible presence of enteric pathogens.The enterococci test is recommended as a measure of ambient fresh and marine recreational water quality. Epidemiological studies have led to the development of criteria which can be used to promulgate recreational water standards based on established relationships between health effects and water quality. The significance of finding enterococci in recreational fresh or marine water samples is the direct relationship between the density of enterococci and the risk of gastrointestinal illness associated with swimming in the water. Method 1106.1 for enterococci can be applied to potable, fresh, estuarine, marine, and shellfish growing waters. Method 1106.1 was submitted to interlaboratory validation in disinfected wastewater matrices. Based on the 60.5% false negative confirmation rate for unspiked disinfected wastewater, an estimated 14.1% of total colonies observed during the study would have been incorrectly identified as non-enterococci colonies. As a result, Method 1106.1 is not approved for the analysis of disinfected wastewater. A summary of false positive and negative results are provided. Detailed study results are provided in the validation study report. Laboratories wishing to test for enterococci in wastewater using a membrane filtration method are referred to EPA Method 1600.