It is the formation of insoluble calcium and magnesium salts from hard water. Only forms with Anionic soaps, not nonionic.
Areas where there chalky deposits in the tap water or in deslinated water...
We keep a squirty bottle of washing up liquid (Ecover) beside our bath and a sponge with a rough green back. We get out of the bath, pull the plug and wipe the bath around with the sponge. As the...