Abstract: Apparatus for disinfecting fluid, the apparatus including a preheat heat exchanger (4) and a disinfection tank (5). The preheat exchanger heats the fluid to a first temperature and includes a first inlet for receiving the fluid (2), a first outlet for supplying preheated fluid at the first temperature, a second inlet for receiving disinfected fluid substantially at a second temperature and a second outlet for supplying the disinfected fluid (3). The disinfection tank heats the fluid to a second temperature and includes a heat source (10), an inlet for receiving the preheated fluid, a heat exchanger coupled to the inlet for heating the preheated fluid to a second temperature to thereby disinfect the fluid (11) and, an outlet coupled to the heat exchanger for providing the disinfected fluid to the second inlet of the preheat heat exchanger.