Water is at once simple and complex.
The configuration of these building blocks produces a molecule with almost magical properties. The ice we skate on in winter is water in its solid form. Unlike most substances, which are densest in their solid state, ice is less dense than water and thus floats. If this were not the case, lakes and rivers would freeze from the bottom up. Fish could not survive, and it is unlikely that rivers and lakes in northern countries would ever completely thaw.