A common question to get about marine animals is “what do they drink”? Do they find a fresh water source and drink from that or do the whales put their heads out in the rain to drink rain water?
The answer is: they do not drink water like land animals do, as they don’t risk dehydration from the sun. This goes for all the marine mammals like whales, dolphins, seals etc. The way they get water is through their food. Most marine mammals will eat fish, and depending on what species of fish it is some have more water in them than others. Most of the whales and dolphins are picky on what they eat, they have the food they prefer and the food they need to eat. Female dolphins that are pregnant normally needs fish that have a high amount of protein and fat for the calf growing inside of them. When they have given birth the females will change over to food that has a higher water content to be able to produce milk for her calf. She will use her body fat reservoir and the water in the food to create this milk.
Marine birds and reptiles have another way of dealing with saltwater. Some will go for the type of food that has extra water, although others doesn’t go for water rich food, they drink saltwater instead. Since birds fly in the sun, and reptiles spend time on land, they can become dehydrated. How can they drink saltwater? The birds that drink saltwater have salt glands at the base of their beaks where they can excrete the extra salt. The whole proses is complicated, but in easy words they have a salt pump (sodium-potassium pump), that removes the salt from the blood and aggregate the salt in the salt gland from where it will be excreted in a concentrated solution. In the birds the excretion is at the base of the beak and they will get it out by shaking their heads, that’s why it sometimes looks like birds are crying, but it’s only the salt coming out. Marine reptiles like sea turtles and marine Iguanas also need to excrete the extra salt they consume. They get the extra salt through their food and are often grazers that will eat sea grass or algae with a high salt concentration. They have a salt gland that sits in the nostrils, so they will blow hard through their nose to get rid of the extra salt, this looks like a big smoke cloud.
As a conclusion, marine mammals regulate their water intake with their food while the marine birds and reptiles can drink saltwater but will excrete it through there special glands.