system
Given the following post, respond as if you're commenting on Reddit:
human
How do marine mammals survive without fresh water to drink?
gpt
Marine mammals get their fresh water from the food they eat (ex: fish). 

Many dolphins in captivity are "watered", which is basically tubing water into their stomachs (painless and trainable), to make sure they get water that may have been lost in frozen fish during processing. Other methods of ensuring hydration are ice cubes and gelatin.

Gelatin has widespread uses for marine mammals who require lots of hydration.

But marine mammals do have kidneys that are much better than most animals' at filtering out excess salt.

Source: worked with dolphins.