Integrated collector storage (ICS) solar water heaters with stationary compound parabolic concentrating (CPC) reflectors are designed and test results are presented. The systems consist of single and double cylindrical horizontal tanks properly placed in truncated symmetric and asymmetric CPC reflector troughs. The suggested designs aim to achieve low cost systems with improved performance by the reduction of their thermal losses and the increase of water temperature rise by using the non-uniform distribution of solar radiation on the absorber surface. Four experimental models were constructed and tested outdoors to determine their mean daily efficiency and thermal losses during the night, Test results showed that asymmetric CPC reflectors contribute to lower thermal losses and the two connected in series cylindrical storage tanks result in effective water temperature stratification. The system with the single cylindrical storage tank and the symmetric CPC reflector performs satisfactorily during the day as well as during the night and regarding its simpler design it could be considered cost effective among the studied ICS systems. A typical thermosiphonic system with flat plate collector was tested for performance comparison, by which the improved daily efficiency of ICS systems and also their moderate water storage heat preservation during the night were confirmed, (C) 2002 Elsevier Science Ltd. All rights reserved.