This paper presents the results of an experimental study conducted in a water solar flat plate collector with laminar flow conditions to analyze the flow distribution through the collector. LDA-measurements were carried out to determine the discharge in each riser, as well as pressure measurements to investigate the relation between junction losses and the local Reynolds number. Analytical calculations based on the measured relations are used in a sensitivity analysis to explain the various possible flow distributions in solar collectors. In addition, a simple parametric approach to predict the flow distribution without performing a pipe network calculation has been realized. (C) 2003 Elsevier Science Ltd. All rights reserved.