Fundamentally, water pollution is the accumulation of one or more substances in a body of water to such a degree that it causes problems for people and/or animals. Here is the United Nations' definition:
"The introduction by man, directly or indirectly, of substances or energy into the marine environment (including estuaries) resulting in such deleterious effects as harm to living resources, hazards to human health, hindrance to marine activities, including fishing, impairment of quality for use of sea water and reduction of amenities."
2 BASIC TYPES
Water resources such as oceans, rivers, lakes, streams.
Water stored in underground aquifers.