Water resistant sunscreen protects your skin for 40 minutes of sun exposure. Waterproof sunscreen protects it for 80 minutes. If you are planning on spending all day at the beach or in the pool, remember to reapply! One application will not protect you for the entire day. Also, make sure you are using enough sunscreen to get the job done. Studies have shown individuals use about half the recommended amount of sunscreen the manufacturer used when determining the SPF. The average adult needs about one ounce of sunscreen for adequate protection.