Do whales drink seawater?

Whales spend their entire lives in the ocean. Their bodies are completely adapted to life in the water. Among amazing evolutionary features, whales’ noses (called blowholes) moved to the top of their head so they can breathe easily without having to put their heads out of the water (check our post on blowholes for more details). Whales’ fins also evolved from terrestrial limbs into fully functional fins and fluke, showing how well these creatures can thrive underwater. 

However, have you ever wondered if whales drink? Where do they get their water from? Whales are huge and they need water in their bodies to survive, just like us. Yet, we all know what happens when we’re at the beach, get swept away by a wave, and end up swallowing some water. It tastes awful. It’s so salty and can be dangerous for us since we need to eliminate the salt to stay alive. Our kidneys are not made to process that much salt. They require a lot of water to do so… and it can lead to dehydration. 

Do whales drink seawater?

But then, how can whales get their water? Baleen whales do swallow a bit of water when they feed because they engulf large quantities of food (krill or fish) at a time and end up ingesting some seawater in the process. How could they consume seawater and not get dehydrated like us? Short answer: they do not drink voluntarily it and they can filter seawater salt efficiently.

Whales (whether they are toothed whales or baleen whales) do not voluntarily ingest water. At least not that we really know of. They find another way to “make” their own water. How? By transforming their food into the water.

Water from food?

Metabolic water is what we call the water that comes from breaking down the food (fat, protein, and carbohydrates). When food enters the whale’s body, its metabolism will break it down into nutrients, and then will break down the nutrients into energy and water. Fat is the preferred nutrient to break down since it produces the most water per gram. Also, whales do not sweat so they do not waste precious water.

What happens when they ingest seawater?

If whales ingest seawater, it should not be a big deal because their kidneys are super-efficient at filtering their blood. Scientists believe the magic behind whale kidneys’ efficiency is the length of their tubules that helps with water reabsorption. A marine mammal’s urine can actually be at least twice as salty as seawater! The major drawback is that these big kidneys require a lot of energy to function. 

Can we measure the amount of water that enters a whale’s body?

The question remains unanswered today because it is so hard to measure it in the wild. Some studies have been performed on seals in aquaria but no large whale can be studied in a controlled environment. Do you know how we could do it? Let us know in the comments!

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You can read more here:

• Verlo, A. (2012). Seawater consumption in dehydrated hooded seals (Cystophora cristata) (Master’s thesis, Universitetet i Tromsø).
• Mellanby, K. (1942). Metabolic water and desiccation. Nature, 150(3792), 21-21.