With a chemical treatment, you can completely waterproof a Raspberry Pi and use it submerged.
How to Waterproof Your Raspberry Pi
- Place the Raspberry Pi into your small tub. …
- Pour Corrosion X over the board until it’s submerged. …
- Swirl Corrosion X around in the container for 2-5 mins to make sure the metal soaks up the oil really well and bonds to the metal.
- Put the Raspberry Pi on a paper towel to drip dry…
Source: Tom’s Hardware