Combining the measure of water availability and the socioeconomic capacity to access to it gives new insights in the fields of water resources management and poverty alleviation. This approach has conducted to the definition of Water Poverty Index (WPI) by Sullivan (2002). The methodology initiated by Sullivan and Lawrence for the calculation of this WPI was based on equally weighted average for its five components (Resources, Capacity, Access, Use, and Environment) to produce a single components Indexes scores. The main objective of this paper is to improve this procedure by using an objective weighting scheme. For this purpose we use a principal component analysis of correlation matrix to give more weight to components with larger variance and to discard components with very smaller variance. This improved WPI is applied, thanks to a rich data base collected by our own efforts, on the case of Tunisia. We have obtained good results which could help policy makers to devise better policies to alleviate poverty in the Inland region which was the bed of the begging of the Tunisian revolution.