No electric skateboard is waterproof. However, most of them are water-resistant. Water-resistant boards (from reputable manufacturers/brands) are graded with an IP-56/IP-65 certificate. Boards with this certificate specifically passed hundreds of water tests without catching fire or being damaged in any way.
Updated at 2023-05-25

Skateboard FAQ
Are they waterproof?

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Skateboard FAQ
What is the difference between Longboard & Skateboard?
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Is an E-skateboard good for a first timer?
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Can an E-skateboard be used as a normal skateboard?
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Which is best material for electric skateboard?
Skateboard FAQ