Recently we have developed a model of photovoltaic water pumping systems (PVWPS) for domestic water access in poor rural areas. In this article, we perform a sensitivity analysis over the 14 parameters of this model. We study how the variation of the parameters value influences the model output and the optimal sizing obtained from the model, for both the dry and the wet season. Results indicate that the peak power of the photovoltaic modules, the efficiency of the motor-pump and the tank volume have the highest impact on the model output. Besides, the parameters which significantly influence the optimal sizing are the position of the water entry in the tank, the position of the stop level of the float switch, the distance between the stop and restart levels of the float switch, the height between the floor and the bottom of the tank, and the static water level in the borehole. Finally, the thermal parameters of the PV modules and the hydraulic losses have a small impact on the model output and on the optimal sizing. This study can be useful to companies, governments and non-governmental organizations which install PVWPS for domestic water access. It can help them to determine the accuracy at which a given parameter has to be known to correctly model or size these systems. It can also allow them to evaluate the robustness of PVWPS sizing to parameters variation with time. Finally, it may guide the choice of components made by PVWPS installers.