Indoor wood work benches are typically not waterproof, but outdoor ones sometimes are. This is because workbenches are designed to take the wear and tear from woodworking tools, and waterproof sealants are not useful once they take damage from abrasive or sharp edges. Minor water damage from spills or moisture is removable by sanding, using steel wool, or even with a hairdryer.
Outdoor wood workbenches may use special high-grade sealants to increase their lifespan outdoors, but for maximum weatherproofing, consider covering them with a tarp between uses. You can also apply your own sealants to both indoor and outdoor benches to improve their water resistance.