This rapid review report has identified the wastewater treatment plant (WWTP) options used in emergency settings, with decentralised wastewater treatment systems (DEWATS) and mobile wastewater treatment units performing most effectively and with minimal costs. Examples are taken from refugee camps and internally displaced people (IDP) settlements due to the Iraq war, the Israeli-Palestine conflict, and the civil wars in Syria and Sudan. WWTP options used in Finland, Haiti, Iraq, Jordan, Palestine, Sudan and Turkey are discussed.Lessons learned from China and suggestions for the Rohingya crisis are also included. A lot of available evidence focuses on water treatment plants, pre-assembled Mobile Water Treatment Equipment (MWTE), or modular water treatment kits (to be assembled in the field) which are used to clean water for drinking in emergency systems, which is not within the scope of this review. The WWTP findings listed are based on peer reviewed journals, global funding agency reports, as well as grey literature. Model information is taken from global manufacturers specialising in WWTP production, however, there is a paucity of information describing models used in specific settlements/refugee camps in low-income/slum areas. Senior experts consulted for this review confirm that there are very little published evaluations on affordable wastewater treatment plants used in emergency settings. Although there are reports of systems specifically for women and children, most wastewater treatment plants are in settlements and sites to be used by both genders, therefore the data included in this review is gender-blind. No specific data searches were made for disabled WWTP users.