Water

 was a prized liquid for those who lived under the surface of Ravolox. (TV: The Mysterious Planet)

Water was a seen as a source of great wealth for the Martians. On Mars, great warriors were often entombed in blocks of ice. (PROSE: The Dying Days, AUDIO: Red Dawn)

The rain on a human colony planet appeared to be living water. (PROSE: Pitter-Patter) Kar-Charrat also had sentient water on it. (AUDIO: The Genocide Machine)

In 2059, the Flood infected Bowie Base One's water supply. (TV: The Waters of Mars)

Effect on species
A Thermortian Sand Worm's organs would collapse to sludge if it consumed water. (COMIC: The Forgotten)

Skullions didn't drink water as it "burned" them. They preferred citrus drinks such as orange and lemon juice. (TV: The Man Who Never Was)

Seed pods were resistant to acid, but vulnerable to water. (TV: The Seeds of Death)

A small amount of water was enough to kill a Pyrovile. (TV: The Fires of Pompeii)

Water was fatal to the Vrakons. (COMIC: The Devil's Mouth)