Water
From MediaWiki

Water is a chemical substance.
Fiction
Generation 1
Marvel Comics continuity
Water is so rare on Cybertron that Wideload and Rollbar had never even heard of it.
Cybertron's surface is covered by at least a few seas, but these seas are not of water. The Rust Sea, for example, is a sea of, uh, rust. There are chambers deep inside Cybertron which also run with liquid, but they have been confirmed to be not water.
The Transformers who are unfamiliar with water are likely confused, as several humans later managed to exist without environmental protection gear on Cybertron without drying up like old corn. Not all Transformers are unfamiliar with water; in the very first issue of the Marvel comic, Ironhide mentioned his "water gun," and Bumblebee commented on how his levers "love a good swim."
Cartoon continuity
Water applied to a human's epidermis frees him from the controlling effects of Soundwave's hypnotic ultrasonic suggestions. Auto-Bop
Generation 2
Some Transformers, namely the Aquaspeeders and Stormtroopers, use high-pressure water-cannons as armaments. This is after they apparently re-discovered water, or something.
Notes
- Occasionally, the fleshlings like to hand out minuscule samples of this substance as promotions for their documentary footage of Cybertronians.

