Aims: Concentration of pathogens diluted in large volumes of water is necessary for their detection. An automated concentration system placed online in drinking water distribution systems would facilitate detection and mitigate the risk to public health. Methods and Results: A prototype concentrator based on dead-end hollow fibre ultrafiltration was used to concentrate Bacillus atrophaeus spores directly from tap water. Backflush was used to recover accumulated particulates for analysis. In field tests conducted on a water utility distribution system, 3.2 x 10(4)-1.4 x 10(6) CFU ml(-1) (6.1 x 10(6)-3.0 x 10(8) CFU) were recovered from the filter when 2.9 x 10(7)-1.0 x 10(9) CFU were spiked into the system. Per cent recovery ranged from 21% to 68% for flow volumes of 15-21 l. Tests using spore influent levels < 10 CFU l(-1) (spike < 1000 CFU) yielded 23-40% recovery for volumes > 100 l. Conclusions: B. atrophaeus spores at levels < 10 CFU l(-1) were concentrated directly from tap water using an automated dead-end hollow-fibre ultrafiltration system. Significance and Impact of the Study: The prototype concentrator represents a critical step towards an autonomous system that could be installed in drinking water distribution lines or other critical water lines to facilitate monitoring. Recovered samples can be analysed using standard or rapid biosensor methods.