On average, seawater has a salinity of 3.5%. This means that for every 1 liter (1000mL) of seawater there are 35 grams of common salt (sodium chloride). Water with this level of osmolality[?] is not potable[?].
Even on a ship or island in the middle of the ocean, there can be a "water shortage", meaning a shortage of fresh water. This is described most famously by a line from Samuel Taylor Coleridge's The Rime of the Ancient Mariner:
Seawater can be turned into drinkable water by the process of desalination.
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