Some experts predict that the next wars may be fought not over oil, but water. Water, a renewable resource, is found in abundance around the world. It comprises 70% of the Earth's surface. All living organisms on the planet rely on water to grow. Humans, for example, can survive for about a month without eating, but only a week without drinking water. Unfortunately, the planet's rivers, lakes and oceans are becoming polluted. Because clean water is important but scarcer, countries wanting to ensure a stable supply of it could go to war. The vice-president of the World Bank has said, "If the wars of this century were fought over oil, the wars of the next century will be fought over water." Egypt depends on the Nile for 98% of its water needs, and it has already vowed to go to war with Ethiopia if the country diverts ater from the Blue Nile.

Water can become polluted in a number of ways. Toxic waste from factories is often discharged directly into waterways. Sometimes waste and sewage from residential homes is also pumped directly into lakes or rivers. Manure and other waste from livestock can seep into underground water sources or nearby bodies of water and contaminate them. POower boats emit noxious gas into the water, and some large vessels have spilled oil or other contaminants into the ocean after hitting rough waters or not being kept in top shape.

Contaminants can also enter lakes, rivers and oceans through rain water. Gas emissions from automobiles, factories or other pollution sources can b e absorbed into the atmosphere, and then be released into the rivers or land when it rains. This polluted rainwater is called acid rain. Acid rain can cause deforestation, contaminate rivers and lakes, and even cause damage to buildings.