As a perfect example of Water-Energy-Food nexus, photovoltaic-powered irrigation is a suitable system for farmers of the semi-arid countries of Sahel. This system can be one of the excellent ways to achieve some of the UN Sustainable Development Goals (SDGs) regarding food access, water access and energy access. Mastering the installation, configuration and operation of the solar PV water pumping system regarding the environmental conditions is crucial for resource-saving and efficient use. This study's main objective is to evaluate the efficiency of a direct-coupled photovoltaic water pumping system (PVWPS) through the case study of the most common and demonstrator system installed in a rural area. The equipment has been installed within the CIREG (Climate Information for Integrated Renewable Electricity Generation) project as a demonstrator site at Bonkoukou in Niger (West Africa). The PVWPS efficiency assessment demonstrated that the PV array has been oversized twice. The increasing PV array capacity (i.e., the electric input current) over the manufacturer's prescription of the pumps does not substantially improve the system's performance but leads to lower pump efficiency. Indeed, by doubling the PV array power from 1.5 kWp as suggested by the manufacturer to 3 kWp, the maximum pump output is not significantly different from the one obtained with 1.5 kW (4.2 m3/h versus 3.5 m3/h with just an increase of 20%).