Signs: Hydrophobic extraterrestrials, go home!

In the large list of extraterrestrials invading the world in science-fiction history, those of Signs, the M. Night Shyamalan film from 2002, find themselves among the most incredible because of their allergy to water, which can be suspected along the film and gets confirmed in the end, giving the key for expelling them from our planet.

Life away from water happens to be not impossible but quite difficult to take into consideration for most scientists. If it existed, it would be a sort of life very different to everything we know: water is an essential compound in chemistry due to its neutrality (lack of acidity or alkalinity) and also because it is a universal solvent. Actually, a key point in the search for present or past life on Mars is making clear if liquid water is, or was ever, present on that planet.

Therefore, it seems strange to think of a living thing allergic to water, and much stranger in antropomorphic beings like the little martians from Signs. Nevertheless, even when there could be forms of life, not only not dependent of water, but also hurt by it, it is not at all possible they could invade the Earth.

Apart from the well known fact that three-quarters of the Earth is covered by water, the air we breath is made of water to some extent, a considerable extent actually, as we all get to appreciate the difference between wet climate, in which the air contains more water, and dry climate.

Not only could a hydrophobical extraterrestrial never get wet, then, but the very slight contact with air itself would hurt him: space suits would become indispensible. In any case, their allergy to a compound as common as water would become obvious as soon as they set foot on the planet. No way would they be able to conquer any territory before humans found so easy a way to get rid of them. Others, beside, would find out much earlier than the family in the film, which were good fellows but a bit simple-minded....