As explained in the book Mineral Tolerance of Animals, cats can tolerate more salt in their diet than dogs. But does this mean they can drink seawater without consequences?
It’s generally safe for felines to drink from saltwater pools, which contain around 1/10th of the seawater salt. If they do drink a little bit of water directly from the sea, nothing bad will happen. Much like people, they can tolerate it pretty well.
However, it’s not safe and in no way recommended for cats to drink any bigger amount of seawater. If that happens, an urgent visit to the vet is due. To prevent cats from drinking seawater, a bowl of fresh water should be placed nearby so they are not tempted when thirst strikes.