The government of Nepal has established five Regional Monitoring and Supervision Offices (RMSO) and the National Management Information Project (NMIP, since 2004), for decision-making in Water, Sanitation and Hygiene (WASH) sector. The Nepal has committed to ensuring that a minimum of 53% of the population will have access to sanitation by 2015 and will achieve 100% sanitation by 2017 and recent (2011) coverage were 80% water and 43% sanitation. The leave of toilet coverage has increased from approximately 6% in 1990 to 43% as of 2009/2010, annual growth rate each year’s therefore equates 1.9%. If the present trend continues, the toilet coverage will be only 80% against the national target of 100% by 2017. In addition, 25.4% people are poor and 29% are landless, besides sanitation policy of Nepal does not provide subsidies for the poor and needy to install latrines. It is however rather unclear how this system works in practice for decision making on the basis of present data, models and tools which has been implemented through the existing monitoring and reporting system of RMSO/NMIP. This qualitative study was conducted through participant observation method to assess the gaps between design and practical outcomes of data, models and tools to minimize performance dilemma. The findings shows that RMSO/NMIP has been using inappropriate many formats for data collection, conducting different methodologies at a same time and data being double counted in some cases that influence poor decision making in this sector. The study has found some gaps; like data collecting, data use for project management and follow up, processing and presenting, developing indicator and survey and forth, and also offer some recommendations to overcome complexities to collect appropriate data at WASH sector in Nepal.