Apple does not exactly advertise the Apple Watch as being rugged or waterproof. That does not mean that your smartwatch dies as soon as it comes in contact with liquids. The folks at DC Rainmaker tested an Apple Watch in a waterproofing chamber to 40 meters and found out that the watch can survive underwater.
How about swimming? Should you swim with your Apple Watch? In the below video, you can see how the Apple Watch fared after a 25-minute session in the pool. Heart rate monitoring in the pool is not going to be accurate, but the watch did perform well otherwise.
The Apple Watch may not be the toughest smartwatch on the market. But it can handle water exposure. If you are too worried about damaging it, you should probably invest in a rugged case for it.