Remove the shower curtain from the rod, and remove each clip from the top edge of the curtain.
Place the shower curtain in the washing machine. Add 1 cup of baking soda to the washing machine. If the care label suggests laundry detergent, add an appropriate amount of laundry detergent for the size of the wash load. If you lack a care label on your shower curtain, wash it alone with only baking soda to see if this is enough to clean the curtain. Set the water temperature to warm, and start the washing machine.
Remove the shower curtain from the washing machine after the wash cycle finishes. Check to see if it is clean.
If stains remain, place the shower curtain back in the washing machine and add 1 tablespoon of chlorine bleach to the bleach dispenser. Set the water temperature to warm, and wash the shower curtain a second time. Adding a nominal amount of bleach should not harm the color-fastness of the shower curtain and may be effective at removing stubborn mildew stains. Start the washing machine.
Remove the shower curtain from the washing machine. Dry the shower curtain in the dryer or dry it in the sunshine on a clothesline. If stubborn mildew stains persist, dry the shower curtain in the sun to help remove these stains.