Published at Sunday, August 05th 2018, 20:17:33 PM by Sally Myers. Shower Curtain. Even though a lot of water splashes on a bathroom curtain, it gets dirty after a while and needs cleaning. So what makes them dirty? Hard water and soap scum slowly builds up on the curtains and remains even after they dry off. These dry soap deposits give off a moldy smell over time and are visible as ugly spots on the curtains.