Mix 1 part vinegar to 3 parts water in a spray bottle, and when you’re finished your shower, mist the wet side of the curtain, top to bottom, flip over the edges and mist those and the bottom side of the curtain that touches the tub, as well as the side of the tub.

And at the risk of re-igniting the dreaded washcloth wars; to keep washcloths fresher, squish them around with soap after using, rinse, and spray with your vinegar solution. Additional rinse is optional.