Water and natural gas trapped within this clay are squeezed out by the rapid compression of the clay and enter the more porous sand or silt deposits. This chapter discusses advanced water treatment technologies used in hydraulic fracturing to treat oil and gas produced wastewater. In fracking operations, depending on location, water may be the most valuable and elusive operational substance used. Produced wastewater is extracted at an average rate of 2.4 billion gallons per day, and over 80% of production occurs in the western United States. Cost calculations for water sourcing, transportation, storage, treatment, and disposal are not commonly presented on a whole-cost basis. Water transportation is required to move water onsite for well development and offsite for treatment or disposal. Water quality varies widely in quantity and quality—depending on the method of extraction, type of oil and gas reservoir, geographical location, and the geochemistry of the producing formation.