According to the internet, when confronted with a shower curtain or shower curtain liner that has become icky with accumulated dirt, limescale and hard water deposits, mildew and mold, soap scum, and serratia marcescens bacteria (!) … many people will just throw it away and buy a new one. Even members of my own family would do this!
However, a spin in the washing machine will make shower curtains and liners as good as new and repeated washings can add months or even years to their useful lives. Just put them into the washing machine with a few heavy towels (especially for top-loading machines, which can tear up shower curtains without the towels to act as padding and buffers) and add the usual amount of detergent. As a booster, add about a half cup of ammonia (my favorite), or some baking soda, borax, vinegar, or bleach. [Of course, never use ammonia and bleach together.] Run the machine on the longest cycle with hot water. You might pause the machine for some additional soak time. There’s no need for a high-speed spin. Don’t put the shower curtain in the dryer. Just re-hang it in the bathroom and admire it as it dries.
You can also admire the money that stays in your bank account each time you do this. A new shower curtain might cost at least $8. Washing it in your home washing machine costs about 50¢.
If you have a mildew, mold, and serratia marcescens problem in your bath and shower area, a fan in the bathroom might help.