When you first purchase waterproof, breathable rain gear, it is coated with a durable water repellant coating known as DWR. This chemical is what makes the water bead off the surface of the clothes and prevents you from getting wet. If you notice your garments are not as repellant as when you first bought them, you can purchase and re-apply a water repellant spray.
Purchase a durable water-repellant coating spray.
Wash your garment in the washing machine, but do not dry it.
Wet the piece of clothing with a spray-on water-repellant solution. Follow the directions from the manufacturer on how much product to use and whether or not to apply the product before the washing process.
Dry the clothing in the dryer on a medium heat setting.
Run your washing machine with nothing in it to remove any product that might be left behind.