The polarity of water is the net result of the overall negative charge of the oxygen atom and the overall positive charges of the two hydrogen atoms. The outcome is a difference in charge, or polarity, from one end of the molecule to the other.
According to the State of Utah Division of Water Resources, a water molecule is polar because the oxygen atom at the top of the molecule has a more negative charge, while the bottom of the molecule, where the hydrogen atoms are found, has a more positive charge. The molecule has an overall neutral charge because the two charges cancel each other out, but the charges are not evenly distributed across the molecule. Molecules of water are attracted to each other through these differences in polarity, forming the important hydrogen bonds that give water many of its unique properties.
The polar nature of water makes it almost a universal solvent; the negative and positive poles of the molecule react with other molecules to break them apart. The polarity of water is also the reason that ice floats. As the water molecules freeze, the hydrogen bonds between them leave gaps between the molecules, decreasing the density and causing the ice to become lighter than an identical volume of water.