Did you know that elephants drink up to 50 gallons of water per day? If they don't their body has biochemical and chemical reactions.
Elephants live in very hot and dry climate so they need to take in more water than what they excrete through their urine and what they evaporate through their skin and airway passage when they breathe. The hotter and dryer the environment the more water they loose because of evaporation. This is true of all mammals.
I remember when we were in Israel, the tour guide has us drink a 64 oz bottle every hour! We were also suggested we eat food that had a high content of water. Humans need water every couple of days to survive.
Back to elephants.... because of their large trunk they are able to suck in a couple of gallons at a time. Although, unlike humans, they are able to go 4 days without drinking water, but then they will take in those 50 gallons of water within one day. These terrestrial animals also have pouches in their throat where they are able to store water.