In photovoltaic (PV) water pumping design, the accurate prediction of the water flow is a key step for optimized implementation and system robustness. This paper presents a model to characterize the motor-pumps subsystems used in PV pumping installations. The model expresses the water flow output (Q) directly as a function of the electrical power input (P) to the motor-pump, for different total heads. The actual model is developed using the experimental results obtained by the use of several motor-pump subsystems of different types and technologies. This work details the investigations concerning centrifugal and positive displacement motor-pump subsystems. The experimental tests are used to validate the developed model. Based on the motor-pump subsystem model, a method is proposed to estimate the amount of carbon dioxide (CO2) emissions saved by the use of water pumping facilities powered by a photovoltaic array instead of diesel fuelled generators. This work shows that the dissemination of PV water systems not only improves the living conditions in remote areas, but is also environment friendly. (C) 2010 Elsevier Ltd. All rights reserved.