IWE AC1 has been developed as an antiscalant for use in Reverse Osmosis and NanoFiltration systems using natural and process feed-waters with particularly high levels of barium sulphate and calcium carbonate. It is also effective against other common scaling species. The strong threshold properties exhibited by IWE AC1 against barium sulphate enable membrane systems to be operated at their optimum recovery rate. This reduces the amount of feed water needed and the volume of reject water for disposal. Consequently, significant capital and consumable cost savings can be made.