The availability of safe and clean water is decreasing day by day, which is expected to increase in the coming decades. To address this problem, various water purification technologies have been adopted. Among the various concepts proposed, carbon nanotube (CNT) based water treatment technologies are the most promising because of its large surface area, high aspect ratio, greater chemical reactivity, lower cost, and energy, less chemical mass and impact on the environment. Therefore, research development and commercial interests in CNT are growing worldwide to treat water contaminants, which have huge impacts on the entire living systems including terrestrial, aquatic and aerial flora and fauna. This review discussed most of the effective CNT based water purification technologies such as adsorption, hybrid catalysis, desalination, disinfection, sensing and monitoring of three major classes such as organic, inorganic and biological water pollutants. In addition, promises, facts and challenges of these novel technologies have been critically analyzed. Special importance has been given in the transformation of environmental CNT, which could alter their generic properties, movement, cellular uptake and potential toxicity of the material in the living systems. This review would serve as a comprehensive reference source for hydrologists, membrane technologists, environmentalists and industrialists to eradicate pure water crisis in the near future. (C) 2014 Elsevier B.V. All rights reserved.