How Pollution Occurs
Pollution can enter at any stage in the water cycle. When we pollute the air we pollute the water vapor that is present. For example, sulphur dioxide and nitrogen oxides from the burning of coal and oil form sulphuric and nitric acid when they mix with water vapor and oxygen. The acidic water vapor can be transported thousands of miles and fall as acid rain. Dangerous chemicals in pesticides (e.g. dieldrin) also travel by air (about 80% of the pollution of lake Superior occurs in this way).

Pollution of the land frequently results in the pollution of rivers and seas. This occurs when rainwater washes fertilizers and pesticides into seas and rivers or the chemicals can seep into ground water.

"Water has a cycle all its own that is beyond our control. The rain that falls on all, rich and poor alike, reminds us that creation is a gift entrusted to our care." We need to realize that we have a finite amount of water and a growing world population. If we do not start using it with great care instead of wasting it, polluting it or treating it as a convenient dumping ground we will be endangering ourselves and all forms of life.

Points to consider
More than half of the world's major rivers are being depleted or polluted and by 2025, two thirds of the world's population may face serious water shortages. Fortune Magazine (May 2000) stated: "Water promises to be to the 21st century what oil was to the 20th century: the precious commodity that determines the wealth of nations." However, we have an alternative to oil whereas water has no substitute.