Coconut water was traditionally sold in the tropics in the form of green, smooth coconuts. The young green coconuts can be opened with a machete, and then you can drink the coconut water with a straw. If the coconut isnʼt fresh, the coconut water may taste sour. In Europe and the United States, you can now buy coconut water in Tetra Paks or cans.
From Wikipedia: “Coconut water is the clear liquid inside young green coconuts (fruits of the coconut palm). In early development, it serves as a suspension for the endosperm of the coconut during the nuclear phase of development. As growing continues, the endosperm matures into its cellular phase and deposits into the rind of the coconut meat.”
“Fresh coconuts are typically harvested from the tree while they are green. A hole may be bored into the coconut to provide access to the liquid and meat. In young coconuts, the liquid and air may be under some pressure and may spray slightly when the inner husk is first penetrated. Coconuts which have fallen to the ground are susceptible to rot and damage from insects or animals.”
“Providing 19 calories in a 100 ml amount, coconut water is 95% water and 4% carbohydrates, with protein and total fat content under 1% each. Coconut water contains no vitamins or dietary minerals in significant content.”
“Coconut water has long been a popular drink in the tropical countries where it is available fresh, canned, or bottled.
Coconuts for drinking are served fresh, chilled or packaged in many places. They are often sold by street vendors who cut them open with machetes or similar implements in front of customers. Processed coconut water for retail can be found in ordinary cans, Tetra Paks, or plastic bottles, sometimes with coconut pulp or coconut jelly included.
Coconut water can be fermented to produce coconut vinegar. It is also used to make nata de coco, a jelly-like food.”
“On islands without water sources, three to six coconuts are needed per person to meet their fluid requirements. Drinking coconut water in place of water is common on islands such as the Maluku and Caroline Islands. Either the coconut water is drunk raw or fermented to make coconut wine. The fermented juice has a bitter taste. Fermented coconut water is also used to distill spirits. You can estimate how long a coconut has been stored by the amount of water it contains. When coconuts are fresh, they contain more coconut water.*”
“Coconut water has been used rarely as an intravenous rehydration fluid when medical saline was unavailable. The story of coconut water being similar to human blood plasma originated during World War II when British and Japanese patients were given coconut water intravenously in an emergency because saline was unavailable. Since then, this rehydration technique has been used only for short-term emergency situations in remote locations where plasma is not available.
Although substituting coconut water for saline is not recommended by physicians today, it was a common practice during the Khmer Rouge regime in Cambodia from 1975 to 1979. The Documentation Center of Cambodia cited the practice of allowing untrained nurses to administer green coconut water during the Pol Pot regime as a crime against humanity.”
“Coconut water has been used in the folk medicine practices of Jamaica for such uses as the treatment of diarrhea.”
The coconut water from the brown coconuts that are sold for the coconut meat in supermarkets often tastes sour and spoiled. It does not have a taste comparable to that of the coconut water from young coconuts.
Note (italics): * = Translation from a German Wikipedia entry