Water purification is an important practice to protect human health from contaminated water sources. A water purification system is a closed system that filters impure water through various physical and chemical processes. Water is run through a series of filters, wherein impurities are collected such as sediments, dissolved, and suspended particles, dissolved oils, and others. It then goes through a series of filtration processes where it gets purified again. This purified water is then used for drinking, cooking, washing, bathing, and other domestic uses.

Water purification has gained importance since the dawn of industrialization and the growth of towns. Industrial chemicals have contaminated most water sources, which lead to several water-related diseases such as diarrhea, cholera, dysentery, etc. The most common uses of water purification technology are water purification for individual consumption (for personal use), to provide water for industrial and municipal purposes, and to treat water pollution. The major applications of water purification technologies are filtration of solids, liquid suspension of water, reverse osmosis, ion exchange, and submicron filtering. Carbon nano-materials, particularly CNTs, are being researched for their applications in water purification for residential, commercial, and industrial applications.