system
Given the following post, respond as if you're commenting on Reddit:
human
How do fish/whales/dolphins/any aquatic life drink?
gpt
Mostly they don't.

Marine mammals get a lot of their water from their food. They tend to live on meat, because blood and body fluids are a lot less salty than seawater. 

Water is also produced as a byproduct of metabolism. When nutrient molecules are broken down to release energy, the largest byproducts are CO2 and water. (For example, if you eat 100 grams of dry sugar, your body will break it down into 60 grams of water and some CO2.)

Marine mammals are also good at conserving the water in their bodies. They have large and efficient kidneys, which create concentrated urine and prevent them from losing too much water. And, because they breathe so slowly, they don't lose as much water in their breath as we do. (An average adult human loses 12 ounces of water per day just by evaporation through the lungs.)

It's hard to be completely sure, but we think that if marine mammals get enough fresh food, they never need to drink at all.