This study presents a simulation tool for the design optimization of Integrated Collector Storage (ICS) solar water heaters using a prototype solar device as reference. The prototype is a commercially available ICS with Compound Parabolic Concentrating (CPC) reflector, installed in the island of Crete, Greece. The aim of this study is to evaluate the optimal sizing of the CPC reflector, aiming at the highest performance of the system, the lowest environmental impacts and the minimization of the production cost. For the environmental profile of the model, Life Cycle Assessment (LCA) was employed. The implemented multi objective nonlinear optimum design of the ICS systems based on the results of the LCA. The environmental parameters in operation mode were evaluated using additional subroutines and functions of the code, which based on RETScreen Expert software examples. The analysis was implemented for different reflector configurations and storage types. The investigated configurations were compared with previous ICS models, in order to define the design specifications for the fabrication of new solar devices. The results imply that the redesigned models improve the energy and environmental performance of the original systems whilst at the same time the total production cost was minimized. (C) 2019 Elsevier Ltd. All rights reserved.