This paper presents the findings from SNV (Netherlands Development Organisation) Laos of the Functionality of Rural Water Supply (FRWS) programme baseline conducted in 2013 in Atsaphone and Phin districts of Savannakhet province. The baseline applied Principal Components Analysis (PCA) to identify the poorest households enabling analysis of household service levels disaggregated by wealth quintile as well as other demographic characteristics. The paper explains why PCA was adopted, practicalities of applying it in the field, and lessons learnt from the process. The resulting baseline findings allow identification of the aspects of rural water supply (RWS) functionality which affect the poorest households enabling SNV to design its programme to meet the needs of the most vulnerable