a water source in fluid communication with a conduit that is fluidly connected to a vessel, wherein the vessel comprises a housing, an inlet in fluid communication with the housing and the conduit, an outlet, and a solid phase chlorine containing material in the form of tablets and at a solids fraction of 40 to 90 percent stackedly arranged within the housing;

an acid source downstream from the water source in fluid communication with the conduit configured to provide the water source with a pH of 2 to 5, wherein the acid source comprises:

i) an electrochemical acidification cell comprising a plurality of compartments, wherein at least one compartment electrolytically produces an acid from an inorganic salt; or

ii) a cation exchange cartridge in fluid communication with an inorganic salt solution, wherein the cation exchange column comprises a cation exchange resin in a hydrogen form; and

a chlorite ion source in fluid communication with the conduit downstream from the acid source configured to form an acidified chlorite feedstream comprising chlorous acid, wherein the inlet is configured to direct the acidified chlorite feedstream comprising the chlorous acid at a lowermost one of the solid phase chlorine containing tablets such that uppermost solid phase chlorine containing tablets are substantially undissolved during operation and are gravity fed to a lower position as the lowermost tablets are dissolved, wherein the solid phase chlorine containing material has physical and chemical properties that are selected so that a reaction rate is greater than an erosion rate, wherein the system is effective to convert chlorite ions in the chlorite ion source to chlorine dioxide at greater than 90% efficiency.