Water

Water was a prized liquid for those who lived under the surface of Ravolox. (DW: 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. (NA: The Dying Days, BFA: Red Dawn)

On planets like Kar-Charrat, water was a form of sentient life in itself. (BFA: The Genocide Machine, DWAN: Pitter-Patter)

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

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

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

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

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

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