Water pollution can be classified by several criteria:
1. Time in which the un-purifier agent is acting
a.permanentă or systematic;
2.Concentration and composition of the water:
a. reduction of the use capacity
b. changing composition and physical appearance of water;
c.serious pollution, which makes improper for use;
d.serious pollution with toxic substances.3.Production of pollution: a.naturală; b.artificial (anthropogenic).
4.Nature of un-purifier substances: a.physical pollution (pollution due to thermal water); b. chemical pollution(pollution from oil residues, phenols, detergents, pesticides, carcinogens, chemicals specific to industries); c.Biological pollution (pollution with pathogenic bacteria, pathogenic yeasts,parasites worms, coliforms bodies , saprophytic bacteria, fungus, algae, etc.). d.radioactive pollution. The phenomena of water pollution may take place:
-at surface (eg pollution with oil products);
-volume ( appear to suspension pollutants).