Why is a compound as common as water considered a "weird" chemical substance?

Water contains hydrogen bonds between the molecules which means that it will remain as a liquid at much higher temperatures than you would expect. This also enables the molecules to 'stick' together and gives water surface tension. The way that water forms into a solid also means that the solid of water (ice) is much less dense than the liquid, allowing it to float.

Compare the normal boiling point of water to that of #CH_4#, #SiH_4#, #HF#, #H_2S#, or #PH_3#. The boiling point of water is disproportionately high. This is also unusual in that water has a very small molecular mass (and thus little possibility of #"van der Waals interactions"#.

And now compare the density of liquid water to the density of solid water. Icebergs float in the ocean! I grant that things are more buoyant in salty water, however, ice cubes also float in ice-water or in your gin and tonic. This is highly unusual, in that, save water, there are very few substances that as liquids are DENSER than their solid phases.

I would consult a textbook on the unusual properties of water. These properties are largely the result of the propensity of the water to #"hydrogen-bond"# intermolecularly.