Overall, this study aims to achieve absolute quantification for live microbial cells in beach water. To achieve this, propidium monoazide (PMA) dye was used at the sample pre-treatment stage to remove relic DNAs. A cellular bacterial internal standard of known abundances (spike-in) was used for calibration in the absolute quantification of live microbial cells. Applying this method, we conducted a quantitative microbial risk assessment (QMRA) for swimming in 4 marine beach waters in Hong Kong and assessed the microbial risks, in the respect of resistome risks, associated with swimming in these beach waters.