Halo Sport 2 is not waterproof. Halo Sport 2 is designed to hold up to sweat and small amounts of water. Do not wear Halo Sport 2 in the rain or submerge it in water.
Although the headset cannot be worn in the water, it can still be used as a training tool for watersports! Check out this article for more information: How can I use Halo Sport for swimming?
Keeping your headset dry
When wetting your Primer Band before a session, please take care to prevent water from getting inside of your headset. For best results, wet your Primer Band and dry off the back before inserting it into the headset. When your Neuropriming session is complete, remove the Primers and dry off your headset with a light cloth. Place your headset in a clean, dry environment.