system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Do sea mammals need to drink water? If so how to they avoid dehydration from the sodium?
gpt
They generally don't drink seawater.  They metabolize water from the food that they eat.  Seals and sea lions occasionally drink seawater and their urine is many times saltier than that of most mammals, their bodies are able to filter out the salt.  The actual salt content of their blood is not particularly different from humans or other land mammals.