Is water a polar or a non-polar molecule? What is the consequence of that characteristic for the function of water as solvent?

Water is made of two atoms of hydrogen attached by covalent bond with single central atom of oxygen making an angular spatial structure. The hydrogen atoms "lend" electrons to the oxygen and consequently this atom becomes more negative whereas the hydrogens become more positive. The spatial geometry of the water molecule makes it a polar molecule, with negative and positive poles.

Water is a good solvent for polar substances because the electrical activity (attraction and repulsion) of its poles helps the separation and the mixing of these substances, giving them more movement and therefore increasing the number of molecular collisions and the speed of chemical reactions. On the other hand, water is not good as a solvent for non-polar substances.

Polarity is one of the water properties.

Water Properties and Mineral Salts: water polarity