Produced Water (PW) is the water trapped in underground formations that is brought to the surface along with oil or gas in extraction operations and it is the highest volume liquid waste stream generated in the petroleum industry. Figures published in 2011 indicate that globally, 69.8 billion barrels of PW were generated from oil and gas operations in 2007, with only a small percentage treated for beneficial reuse.

Historically, the treatment of PW has been limited to free oil removal and discharge in water bodies or deep injection in disposal wells. However, due to more severe legislation or geological restrictions on site, the trend will be for a greater fraction of the PW to be extensively treated and ultimately recycled or reused for different end uses. Also, opportunities are arising to reuse the treated PW in, for instance, enhanced oil recovery (EOR) processes or for steam assisted gravity drainage (SAGD) applications. This will imply removal of additional contaminants such as dissolved organics and salts and hence need more advanced water treatment technologies.