With the aim to increase the quantity of absorbed energy and improve optical and thermal performances, a new design of an integrated collector storage (ICS) solar water heater combined with a compound parabolic concentrator (CPC) is presented. This model consists of two concentrating stages. The upper part contains two symmetrical parabolic sections with focal axes rotated by theta = 48 degrees in counterclockwise sens and theta = -48 degrees in clockwise sens from vertical plane. The lower part is constituted by three involute reflectors. Its cylindrical storage tank covers the triangle formed by the three involute parts center's. The geometric concentration is about 1.34. This design has a strong connection with a previous study where an old ICS system was designed and experimentally tested. A ray-tracing model was developed to simulate the reflection of the direct solar radiation on the CPC reflectors at different angles of incidence and compute the absorbed solar radiation distribution on the absorber surface. The obtained results, when compared with the old experimented model differing on the design of the lower stage concentrator, showed a significant improvement in optical efficiency, the distribution of the absorbed energy regarding the angle of incidence and the temperature level required. (C) 2014 Elsevier Ltd. All rights reserved.