Salt water

Generally, water from the world's oceans and estuaries.

The saltiness of water varies from one body of water to another. It is dependent on how much dilution has occured from rain water, melting glaciers and from rivers flowing into the local part of an estuary.

Salt water from mid-ocean is salty enough that drinking it is of no benefit, even in survival situations. The salts are more concentrated than the salts in one's blood, and the kidneys can not remove free water from salt water that you drink. Rain water caught on a tarp or in the cockpit may taste salty but be dilute enough to be of value to the body.

For those who wonder, and are afraid to ask, urine and blood have the same problem. Once someone is dehydrated, the level of salts in the urine and in the blood does not allow the kidneys to remove free water to relieve dehydration.

Purification of salt water is difficult. See Purification.