Kaben live in salt water. If a crab drank water that is fresh water it will surely die! Many salt water animals cannot properly process fresh water. Likewise many fresh water animals cannot breath salt water. It slowly kills them by poisoning them.
Aquatic animals with the exception of mammals do not actually drink water. They filter oxygen and/or nutrients from water by their gills or some other means.
This sentance is misinformation. While the majority of adults and older children already know this, younger ones taking this course may be misinformed and learn the wrong information.