Human caliciviruses (HuCVs) cause waterborne outbreaks of gastroenteritis. Standard indicators of a safe water supply do not adequately predict contamination of water by viruses, including HuCVs. We developed a method to concentrate and detect HuCVs in water samples by using a cultivable primate calicivirus (Pan-1) as a model. Viable Pan-1 was seeded in different types of water and then filtered with a 1MDS filter, eluted with beef extract (BE), and reconcentrated by polyethylene glycol (PEG) precipitation. The viruses in the final samples were tested by plaque assay or by reverse transcription (RT)-PCR following extraction of the RNA with Trizol. Pan-1 was more sensitive to high-pH treatment than poliovirus was; a pH 9.0 BE solution was found to recover 35% more viable Pan-1 than a pH 9.5 BE solution recovered. Pan-1 was recovered from small volumes of deionized, finished, ground, and surface waters at efficiencies of 94, 73, 67, and 64%, respectively, when samples were assayed after elution without further concentration. When larger volumes of water (up to 40 liters) were tested after elution and concentration with PEG, 38, 19, and 14% of the seeded Pan-1 were recovered from finished, ground, and surface waters, respectively. The limit of detection of Pan-1 by RT-PCR was estimated to be 0.75 to 1.5 PFU in 40 liters of finished water. This method may be adapted for monitoring HuCVs in drinking water and other types of water for public health safety.Diarrhea remains an important disease in both developed and developing countries. Among the different gastroenteritis viruses, Norwalk virus and Norwalk-related viruses, now classified as caliciviruses (CVs), play a major role in nonbacterial outbreaks of acute gastroenteritis (23). Large outbreaks of waterborne acute gastroenteritis caused by human CVs (HuCVs) have been documented; in these outbreaks fecal contamination of drinking water or indirect contamination of water or water products occurred (15,16,18,20,25,26). Unlike many bacterial pathogens, which have been controlled largely by modern water and wastewater treatment practices, the incidence of water-related viral diseases, including gastroenteritis and hepatitis, has remained virtually unchanged over the past several decades (23). Use of bacterial pathogens as indicators of clean and unpolluted water does not predict the safety of water with respect to viral pathogens (8,17,21,24,27). Therefore, development of sensitive methods to monitor enteric viruses in water is necessary.Monitoring water quality by direct detection of human enteric viruses has been difficult because only a few infectious units are required for most human enteric viruses to cause infection. Detection of such low concentrations of viruses in environmental samples usually requires concentration of virus from large volumes of water. Even with viruses highly concentrated from water samples, the methods routinely used to detect enteric viruses in clinical specimens, such as enzyme immune assays and cell culture, still are not sensitive enou...