We look for evidence of water whenever we search for life on other planets - Mars for example. But what is it about this seemingly simple molecule, H2O, that makes it so important for the survival of all plants, animals and even bacteria on Earth?

Water moleculeTaking a closer look at the molecule itself, with its two hydrogen and one oxygen atoms, we see that the atoms are not arranged in a straight line.  It is as if the oxygen is greedy for negatively charged electrons, attracting them from the two hydrogen atoms. This makes the oxygen part more negative and the hydrogen parts more positive.

If oxygen is a red ball and hydrogen is a white ball, water looks a bit like this. Get the idea? We say that water is a polar molecule (unequal charge all around). So what? Well, this polarity turns out to be a really big deal - remember that opposites attract... so water molecules can attract each other (we call these attractions hydrogen bonds) and they are also attracted to other charged molecules.

Hydrogen bonds make water "sticky", letting it flow and giving it unusual heat properties.  They can also explain the really cool trick of water which is to be able to hold solid water (ice) near the surface without letting it sink.

And the polarity of water helps it to dissolve many organic and ionic compounds, which is important for letting them react inside cells or carrying them around the body of the animal (e.g. in the blood) or plant (e.g. in the phloem)

These properties, and more, all help water to support life.