Developing more efficient water processing units for oil and gas production is becoming an industry focus. Water occurs naturally within oil and gas reserves and can also be introduced as part of enhanced oil and gas recovery process. The water involved in oil and gas production is called produced water and is an undesired by-product in that industry. Both onshore and offshore produced water requires large amounts of pumping energy and the costs for water management and disposal are rising. The problem is greatest for old wells and for offshore production. Exciting new technologies are being developed to address these issues and engineering simulation can help.