The board is water-resistant, but not water-proof. If you go through a deep puddle, you are probably in for a bad time. Snow has less likelihood than water of getting inside the board, but you’re more likely to lose traction resulting in a fall. Risky situation either way.
The Onewheel is a beast, it can handle a lot of different terrains and that includes a bit of water here and there. It is generally agreed upon that you should avoid, if possible, riding through puddles and other situations where water can enter the board. While picturesque shots of Onewheeling on the beach through the low tide may look appealing, it’s probably not worth voiding your warranty. Water damage is explicitly not covered in the warranty. Some riders have reported that riding in snow is a bit safer with a treaded tire replacement, but newer riders should exercise more caution if attempting this.
Here’s what water damage on the BMS board looks like after riding through puddles – Photo by Ryan WiTz