Ultima Washing Machine Descaler Regular use helps reduce energy and repair bills. Waitrose Washing Machine Descaler will remove limescale from the heating element in your machine, thus restoring its efficiency and prolonging its life. The descaler will also remove detergent and other deposits from the pump and pipework. In hard water areas, use once a month, to keep your machine in top condition. In soft water areas, use every 3 to 6 months. - Prepare and Use: Directions for use: Empty the machine, open the packet. Pour the whole content of the packet into the drum. Close the machine and run on a normal wash programme without pre-rinse. Suitable only for machines with a stainless steel drum.