Hexane is non-polar. Well at least, mostly nonpolar. London dispersion, a particular type of Van der waals force, should be the biggest factor in the bonding of hexane molecules, hence the low boiling point. Smaller alkanes like ethane have even lower boiling points, because there are less carbons and therefore less places for partial charges to form.
Water is polar. The molecules are subject to Hydrogen bonding which can have bond energy's as high as 30kj/mol. Thats why it has a high bp