Chitosan is an economic material applicable to fields of agriculture, biotechnology, and environmental engineering, especially, in the field of water quality managements. The main mechanisms to remove contaminants in water are adsorption, chelation, precipitation, ion exchange, and various reactive functional groups present on the chitosan surface (e.g., amino or hydroxyl group). This review is to summarize the results of many studies regarding the removing contaminants in water phase (e.g., oily substances, toxic materials, suspended solids, humus, dye materials, heavy metals, non-metals, drugs, and emerging contaminants such as pharmaceuticals and personal care products etc.) by chitosan and derivatives. This review explains the examples of the use of chitosan materials to control these contaminants and introduces the current and potential applications of chitosan in the future of environmental fields.