Water

Cybertron gave up water eons of your Earth years ago.

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.

It cures Scraplets. The Cure!

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 or just not very worldly, 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"; before the Scraplets crisis, Ratbat devised a fuel-harvesting scheme involving an Earthen carwash, which of course used water.

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.

Unicron Trilogy

Cybertron Cartoon

After scanning a fire engine as his new alternate mode, Optimus Prime began carrying a supply of water which he used to extinguish fires and on one occasion a Decepticon warp gate. Inferno Trust Revelation Most of the other Autobots were also capable of carrying water, although their efficacy at extinguishing flames was not as great. Unfinished

Notes

• Occasionally, the fleshlings like to hand out minuscule samples of this substance as promotions for their documentary footage of Cybertronians.