Virtually all rainwear is treated with a durable water repellent (DWR), to make the raincoat repel more water. Most raingear on the market is water resistant and not waterproof. A waterproof coat would be made out of vinyl or rubber.
DWR can wear down over time due to normal wear and tear, oils from skin, dirt and scrapes. Rain wear fabric will need to be retreated. You can purchase a water repellent fabric spray and treat your coat at home.
First wash your raincoat with a gentle detergent such as Forever New Biodegradable Laundry Soap on a gentle cycle or hand wash depending on the garments washing instructions.
Let your coat dry before treating with DWR. Hang your coat outside and spray a thin even layer of DWR per instructions. Let the fresh DWR treatment dry for one or two days.
Next, gently treat you coat with heat. You can tumble dry on low if the garments instructions allow for a tumble dry. Alternatively, you can steam the coat with a clothes steamer or hang the coat in the sun for an hour.
These steps should insure that your rainwear is water repellent and will protect you from the rain.