Abstract: The present invention relates to a method of determining the total organic carbon content (TOC) of a purified water stream in a water purification apparatus having at least a first pump, a first conductivity sensor, an oxidiser, and an oxidiser recirculation circuit having a dedicated second pump, the method comprising at least the steps of: (a) using the first pump to pass a water supply stream through the water purification apparatus, including through the first conductivity sensor and the oxidiser, to provide a purified water stream available for dispense; (b) using the first conductivity sensor to measure a first conductivity value of the water supply stream prior to the oxidiser; (c) stopping the first pump; (d) using the second pump in the oxidiser recirculation circuit to recirculate the water in the oxidiser only through the first conductivity sensor and the oxidiser a plurality of times, (e) using the first conductivity sensor to measure a second conductivity value of the recirculated water; and (

Abstract: There is described a water purifying apparatus comprising: (i) at least one water inlet; (ii) an ultra-violet (UVC) radiation chamber connected to the water inlet(s); (iii) a plurality of UVC light emitting diodes (UVC-LEDs) for the emission of UVC light into the radiation chamber; (iv) a control to operate UVC-LEDs in use, and (v) at least one UVC-LED aging monitor to provide feedback to the control.