Water safety is a major concern for public health and for natural environment preservation. On-site, rapid and unambiguous detection of bacterial pathogens present in waters remains both a scientific and a technical challenge. Taking advantage of the highly discriminating properties of bacteriophages, which specifically infect their bacterial hosts, we propose to use genetically modified virions to develop biosensor tools able to detect human and animal pathogens present in water. To summarize, a reporter protein will be synthesized, and thus detected, only once the specific recognition step between a genetically modified temperate bacteriophage and its bacterial host has occurred. The challenge here lies in combining a sensitive detection of such events with a robust technology for rapid, on-site analysis. We present here two examples of such bacteriophage-based analyzers we designed to detect water contaminations by simply measuring light emission (fluorescence with GFP or bioluminescence with the bacterial luciferase as reporter proteins). In this study, we have constructed and characterized several "phagosensor" prototypes using the HK620 bacteriophage and its host Escherichia coli TD2158 and we successfully adapted this method to Salmonella detection. We developed tests that do not require bacterial growth, since a single 1-hour infection step is sufficient, with no requirement of sample concentration or substrate addition. The fluorescence analyzer is based on a portable flow cytometer allowing the fast, robust and sensitive detection of as few as 10 bacteria per ml. The bioluminescence analyzer is designed to integrate different type of biosensors (bacteriophages, whole cells and antibodies) for inline water monitoring. The bacteriophages-based component proved to be sensitive enough to reliably detect as low as 100 bacteria per ml. Further development will aim to develop phagosensors adapted on demand to the detection of any human or animal pathogen that may be present in water.