The Water Global Practice, under the WSSGSG Utility Turnaround thematic area, has implemented theGlobal Study on WSS Utility Aggregation to provideevidence-based guidance to policy makers and practitionersregarding when, why, and how water and sanitation utilitiescan work together ("aggregate") to successfullydeliver specific policy outcomes, such as better services orlower costs. This work builds on a review of existingliterature and an analysis of both qualitative andquantitative evidence, a global data set of internationaltrends and a series of case studies. Additionally, asdescribed in this report, a statistical analysis based onIB-Net data (which cover 1,306 utilities from more than 140countries) was conducted to better understand the potentialgains from aggregation. The objective of the statisticalanalysis was to empirically assess the performanceconsequences of aggregations. To this end, the statisticalanalysis report uses the whole universe of utilities fromthe IB-Net database to address three core aspects ofaggregations. For more information on the global study,refer to the report, Joining Forces for Better Services?When, Why, and How Water and Sanitation Utilities CanBenefit from Working Together. The accompanying toolkit(accessible at www.worldbank.org/water/aggregationtoolkit),offers a broader set of references and resources to informaggregation processes.