Water is a great solvent (which means that it will dissolve things.) This is because water is a polar molecule. It has a positive and negative end. Because of this, water will disolve other polar molecules such as Salt (NaCl).

Water flows and, therefore, can go just about anywhere. Wherever it goes, water will carry with it the substance or substances it has disolved. It can also transport less desirible materials such as pesticides, and toxic chemicals. Sewer wastewater can contain disease-causing agents. Often sewage and agricultural wastewater contains feritilizers which upset natural ecosystems due to a dramatic increase in growth of algea and other water plants.

Water can cause the erosion of land; destroying valuable soil resources and clogging streams and lakes with silt. Changes in natural river systems by the construction of dams or removing natural wetlands upsets ecosystems. The photograph at the right shows how "dirty" water will look when it is carrying a lot of soil resources. Imagine what this would look like if the water carried pollution instead of dirt!

Extension:

Write a letter to the editor of a local newspaper explaining why you believe the water in your area should be kept contaminant free. Make sure you describe what could be done to fulfill this request.