Water
Water (H2O) was a chemical substance which was often found in a liquid state at temperatures between 273 and 373 Kelvin, its melting and boiling points, respectively. At standard temperature and pressure, water was found in its liquid state. Water was crucial to the existence of life on Earth and to a certain extent to that of most other carbon-based lifeforms. It had some unique properties, such as an unusually high boiling point of 100° C and high adhesion and cohesion properties because of its polar nature and the existence of hydrogen bonding. Water's other states are solid, in the form of ice or snow and gaseous in the form of water vapor. 

Things and beings that lived in or near water were described as aquatic. (, et al.)

During a scan of Aldean DNA, Doctor Beverly Crusher was able to confirm that a rise in atmospheric H2O was not responsible for the Aldeans' sterility. ()

The microbrain referred to Humans as "Ugly giant bags of mostly water!" a description Lieutenant Commander Data considered accurate as Humans were comprised of over 90% water and were surrounded by a flexible container. ()

Kataan was experiencing a constant drought towards the end of the planet's lifetime as its sun was rapidly approaching a nova. Water on the planet had to be rationed and it was considered to construct atmospheric condensers that could reclaim evaporating water from the air. ()

The pre-industrial society of Barkon IV believed that water was one of the four basic elements of the universe, along with fire, sky and rock. Water was sometimes difficult to find in matter, but it was believed that all objects contained water. ()

In 2369, Commander Benjamin Sisko and Ilon Tandro compared the Trill and their symbionts to salt added to water. ()

When Doctor Julian Bashir arrived at the Bajoran village he received a medical emergency call from, he scanned the air, the ground water, and the soil but was not able to find any pollutants. ()

In some regions of the Delta Quadrant, water was scarce and a valued commodity, traded amongst species such as the Kazon and Talaxians. In 2371, Captain Kathryn Janeway used water to bribe Kazon maje Jabin for information concerning the Ocampa. Later, when offered a bath by Tuvok, Neelix delightfully accepted, but was astounded by such an abundance of water that it could be used for the purpose of cleaning in such a manner. ()

After breaking the transwarp threshold in 2372,  Tom Paris started going through the process of hyper-evolution and became allergic to water. ()

A proper amount of water was important to the survival of plants, but too much water could be harmful to certain plants. When Julian Bashir tried to help Miles O'Brien care for Keiko's Idran hybrids, he gave them water when he saw that they were "as dry as a bone," unaware that too much water would rot their roots. ()

In gravitically unstable regions of space (such as the gravitational event horizon of a collapsing planet or star), water can form into long chains of polywater. (; )

Aquatic lifeform types 
Amphibians
Cetaceans
Fish
Turtles

Sentient aquatic species 
Aquan
Bottlenose dolphin
Humpback whale
Megarite
Monean
Xindi-Aquatic

Water drinks

Bodies of water

Art about water 
 20,000 Leagues Under the Sea
 Down the River Light
 "Moon River"

See also 
 Boat
 Fresh water
 Great Material Continuum
 Ground water
 Heavy water
 Hoobishan Baths
 Humidity
 Qui'al Dam
 Seawater
 Water mass

External link 
 

de:Wasser nl:Water
Chemical compounds