Water is a tasteless, odorless and nearly colorless liquid. Water is a molecule with 3 atoms: 2 hydrogen and 1 oxygen. Because oxygen is more electronegative, the oxygen end of the water molecule has a partial negative charge, while the hydrogen end a partial positive charge. So, water molecules are polar, and that is the reason why water can do amazing things.

Human needs water to survive. Water is where our biological reactions take place and also an important metabolite in the process. Because water molecules are polar, they can attract other polar molecules and ions. This polarity gives water the ability to dissolve many substances, making it the "universal solvent". Certain chemical reactions occur when reactants make contact with each other in the water, especially with energy influx, and that was how life began some 4 billion years ago. In our body, water is also the solvent that transports many essential molecules, like oxygen and nutrients, and metabolic waste products, like ammonia and carbon dioxide, in blood and lymphatic vessels and through biological tissues and membranes.

The impact of water pollution on human health is significant. Dirty water may irritate our skin and give us skin diseases. If ingested, dirty water may cause diarrhea and many other diseases. According to US EPA, polluted drinking water can cause health effects, such as gastrointestinal illnesses, nervous system or reproductive effects, and chronic diseases such as cancer.