Provided are a method and system for processing water containing low-molecular-weight organic matter, with which the water containing low-molecular-weight organic matter can be processed with a reverse-osmosis membrane at a high blocking rate. The method for processing water containing low-molecular-weight organic matter includes a reverse-osmosis-membrane processing step for processing water to be processed, which contains low-molecular-weight organic matter having a molecular weight of 200 or less, using a reverse-osmosis membrane, the reverse-osmosis membrane being reformed by bringing a stabilized hypobromous acid composition that contains a bromine-based oxidizer and a sulfamic acid compound into contact with a polyamide-based reverse-osmosis membrane.
