Abstract: A method and system for electrolysis of water to increase the dissolved oxygen content, raise oxidation reduction potential, and perform direct oxidation of dissolved contaminants in situ. This is accomplished by an electrolytic catalytic oxidation (ECO) cell having an innovative configuration of electrodes in a cartridge designed to maximize water contact with an efficiently designed affecting system. The cartridge consisting of multiple mesh electrodes arranged transversely to imposed water flow electrolyzes passing water when energized. The mesh construction of the electrodes allows water flow to be essentially through the electrodes, with a narrow gap set up between cathode and anode to reduce voltage requirements of the system. The cartridge anodes are preferably plated with a mixed metal oxide such as iridium oxide and ruthenium oxide to catalytically improve the production of oxygen.