The purification of water

A chemical composition for the purification of water, which includes a primary mixture of a peroxide compound in the form of an alkaline persulphate, an acidic compound in the form of sodium bisulphate, and an ammonium-based biocidal compound, the mixture containing 45 to 55% (m/m) persulphate compound, 20 to 30% (m/m) sodium bisulphate, and 10 to 20% (m/m) ammonium-based biocidal compound, the alkaline persulphate and the biocidal compound being effective in disinfecting water to be purified and in eradicating algae and bacteria therein, with the acidic compound being effective to lower the pH level of water to be purified. The composition may also include aluminium sulphate as a flocculation aid, upper sulphate for use in the eradication of black algae and a basic compound to act as buffer against high acid levels in water.