A water treatment method to generate potable water and a fertilization or fertigation product is provided. The method comprises the steps of: passing a raw water stream through an anion exchange resin (14a, 14b) to generate a potable water output; regenerating the anion exchange resin (14a, 14b) using a weak potassium chloride solution to generate a product output comprising potassium sulphate, potassium bicarbonate, and preferably also potassium nitrate, suitable for use as or as a precursor to a liquid fertilization or fertigation product.