A formulation for use in the treatment of water and wastewater to remove impurities and harmful micro-organisms comprises a ferrate [Fe(VI)] ion combined with at least one chemical species, preferably a polymerised aluminium species. The ferrate and polymerised aluminium may be combined in a molar ratio ferrate (as Fe) to Al of between 1:2 and 1:4. The composite chemical enables treatment to be carried out at close to neutral pH, typically in the range 6.0 to 8.0, with lower doses compared to the use of ferrate ion alone. In this way, the coagulating/disinfecting properties can be optimised for water treatment.
