A scale and corrosion inhibitor for use in the treatment of water comprises at least one oxyalkylene unit and at least one phosphonate unit (e.g. a unit derived from a mono- or di-phosphonic acid such as VPA or VDPA). Inhibitors according to the present invention have been found to exhibit both scale-inhibiting and corrosion-inhibiting properties, especially in the treatment of cooling water and water used in oilfield applications.
