Effective allocation of investments is crucial to achieve the Water and Sanitation target of the Millennium Development Goals (MDG). The present paper exposes the main results of a detailed study made about the Official Development Assistance (ODA) and the international private investment in the water sector from 1995 to 2004. Public available data sets from the Development Assistance Committee (DAC), the World Bank, and from the Human Development Reports (population and water and sanitation access’ figures) have been collected in a specific database. ODA programmes have been analyzed individually, in order to separate water and sanitation subsectors, since DAC reporting system does not make it directly. The study includes a comparative analysis of public and private international investment; it analyzes the coherence, both geographical and sub sectorial of aid allocation, as well as the terms and conditions of the ODA delivered. Special focus was made on the sanitation subsector. Finally it assesses private participation success in the sector and evaluates cross cutting issues in ODA water programmes. Results of ODA’s analysis show how far donors lag behind their own commitments both in terms of quantity and quality of aid. Data show big geographical inequalities, comparing the share of aid received by regions related to the number of people without access living there. Regardless extremely low coverage in sanitation, donors are not really committed to improve it. Results from international private participation in water and sanitation projects show a little contribution to the achievement of the MDG, as well as a decrease tendency in participation. Complementarities between private and public sector were not significant, if MDG are to be achieved. As a main conclusion of the analysis, we can affirm that there is room for improvements in the water sector’s aid. A global coordination mechanism among donors is needed to ensure more efficient sector’s resources allocation; at the same time, donors should fulfil their own recommendations on terms and conditions of aid. International water and sanitation funds should add on existing national funds in order to effectively increase sector investment. Consideration of private sector’s investments could improve ODA’s allocations. The tiny amount of ODA resources dedicated to sanitation represents a huge contradiction with actual needs.