If there are already signs of mould on the surface, do not simply put the curtain in the washing machine. Instead, soak it in a bucket with a vinegar solution for around an hour and then wash it. To treat mould spots, apply a paste of natron and citric acid, work it in and rinse off. You can then simply put the curtain in the washing machine. Bleach-based laundry detergents can also be used for deep cleaning, but these are not particularly environmentally friendly. For a gentler alternative, pour some vinegar into the fabric conditioner compartment. To tackle intensive soiling and limescale, add a little natron to the washing machine.