Water is one of various needs of human beings that can support life sustainability. In Islam point of view, water is not only basic need, but it is also medium to clean up, to do ablution, and to complete worship. However, clean water and healthy sanitation crisis in Indonesia still happen until now. This research aimed at finding out the mechanism of water and sanitation financing in BMT Mitra Usaha Ummat Sleman and at analyzing the implementation of the decree of National Sharia Council of Indonesian Islam Leader Assembly towards the financing. The research method used was qualitative method by using primary and secondary data. The selection technique of the research subject used purposive sampling method. The data analysis tool used was descriptive-qualitative by using the triangulation as the data validity technique. This research showed that the water and sanitation financing in BMT Mitra Usaha Ummat Sleman that used qardhul hasan contract has been in accordance with the decree of National Sharia Council of Indonesian Islam Leader Assembly while the financing that used murabahah contract has not been entirely in accordance with the decree of National Sharia Council of Indonesian Islam Leader Assembly. The discrepancy could be seen from the financing mechanism and the ownership status of the goods that have not been obvious yet.