A process for treating water containing contaminants comprising the steps of: (a) contacting water to be treated with an inorganic oxidising salt containing manganese or iron for a time effective for oxidising a portion of said contaminants; (b) contacting water treated in oxidation step (a) with at least a chlorine containing agent for disinfection and to generate, in situ and through reaction with chemical compounds produced in pre-oxidation step (a), a coagulant for coagulating oxidised contaminants present in the water; (c) separating coagulated contaminants from the water; and (d) subjecting water to a catalytic oxidation for oxidising residual oxidisable contaminants, said catalytic oxidation being catalysed, in part, by manganese or iron species, depending on the residual selected oxidising salt left in solution in water after oxidation step (a). Permanganates are particularly advantageous inorganic oxidising salts and chlorine dioxide is a particularly preferred chlorine containing disinfecting agent for use in step (b). Apparatus for conducting the process is also disclosed.