Why Water is Called the Universal Solvent? First, we must understand what is solvent and solute?
Solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature. Solute is a substance dissolved in fluid, forming a solution.
Water is a non-ionic polar molecule. So it will dissolve anything which will be similar to it. Actually, the molecule of water is made of two atoms hydrogen and oxygen. Out of these oxygen atoms are negatively charged whereas the atom of hydrogen carries a positive charge. As both the charges are weak, it makes the molecule neutral in itself.
It is because of the same reason that water is able to dissolve all those substances which are of the similar type. Thus, water dissolves more of the substances rather than the liquids in it. It is for the same reasons humans require more of water rather than any other substance.
Source from book:
Hewitt, paul et al. 2007. Conceptual Integrated science. United State Of America: Pearson Education, Inc
Source from internets:
Hydrogen on http://www.purchon.com/chemistry/flash/hydrogen.swf
Oxygen on http://www.chemistrydaily.com/chemistry/Oxygen
Water and organic molecules on http://www.emc.maricopa.edu
Water on http://www.all-water.org/Chemistry.html
Source of pictures:
Kidney on http://lifeblood.anaemiaworld.com
Polar covalent bond on http://3.bp.blogspot.com
Polar and nonpolar molecules on http://www.emc.maricopa.edu
Solute on http://www.chem4kids.com