|Do whales drink salted water? — GR, Montreal, Quebec
No. Marine mammals rely on water obtained from their food. Because they don't sweat, they only lose water through their urine, which they concentrate to minimize the loss of water. What little water these animals do need comes from eating foods that are already relatively low in salt. Most of the lower sea animals, including fish, have active systems—ones that consume ordered energy—for eliminating salt so that when a sea mammal eats one of the lower animals, it inherits that animal's relatively salt-free water. Moreover, metabolizing fats and carbohydrates produces water as a byproduct.