Water is composed of two hydrogen atoms and one oxygen atom. Because of this arrangement, water is a polar molecule - one end has a slight negative charge and the other a slight positive charge. This attribute creates an attraction between water molecules, called a hydrogen bond. The hydrogen bond essentially makes water "sticky", allowing water molecules to bond quite easily with each other as well as with other substances. It is this cohesive property of that enables plants to drink (via capillary action, which pulls water from the plants' roots throughout the entire plant), snowflakes to stick together, and insects to walk on water.



Water's polarity also makes it capable of dissolving many substances. Water is known as a universal solvent because it can dissolve more substances than any other liquid. Many materials are soluble in water, which allows them to be easily dispersed into the environment. Wherever water flows, it takes minerals, nutrients, pollutants, and other chemicals with it. Once chemicals are dissolved in the water they are difficult to remove. This is an important concept when it comes to water pollution and maintaining water quality, as pollutants are very difficult to separate from the water.

Unpolluted water has a pH of 7, which makes it neither acidic nor basic.

Source: http://ga.water.usgs.gov/edu/waterproperties.html