Herein, we demonstrate a facile and economic approach for colorimetric detection of microbial pathogens in drinking water, employing silver-urease interactions. In the presence of harmful pathogens, receptor coated silver nanoparticles (AgNPs) preferentially bind to the bacterial surface and urease catalytically elevates the pH of the solution, which is sensed by a pH responsive chromogenic dye. The assay demarcates bacterial contamination levels up to 102 cells mL-1 in a field-friendly method.