A large population worldwide lives in remote rural communities without access to electrical energy services because of insufficient coverage of the national transmission network due to the distance between these communities. As a result, accessing water resources is a big defiance that prevents improving living conditions for these off-grid rural communities. Photovoltaic water pumping systems (PVWPSs) can be the solution to this critical problem. However, the sustainability of PVWPS needs to be investigated because of the stochastic and unpredictable nature of solar radiation. Therefore, this paper proposes a techno-economic approach to find the optimal capacity configuration of PVWPS, considering its reliability in terms of life cycle cost and loss of load probability. The PVWPS is optimally sized considering the installed PV power capacity and storage water tank volume. Sensitivity analysis in terms of the number of deficient days and curtailed PV power is conducted for two different operating scenarios with and without using a storage tank. This study is applied considering the drinking water needs of a village located in the Western Desert of Egypt. The optimal capacity configuration results of the proposed approach would be feasible and satisfactory, especially in developing countries such as Egypt with infrastructure problems and high solar radiation.