This research target was to improve the thermal efficiency of a solar water heating system (SWHS) coupled with a built-in solar water pump. The designed system consists of 1.58-m(2) flat plate solar collectors, an overhead tank placed at the top level, the larger water storage tank without a heat exchanger at the lower level, and a one-way valve for water circulation control. The discharge heads of I and 2 m were tested. The pump could operate at the collector temperature of about 70-90 degrees C and vapor gage pressure of 10-18 kPa. it was found that water circulation within the SWHS ranged between 15 and 65 I/d depending upon solar intensity and discharge head. Moreover, the max water temperature in the storage tank is around 59 degrees C. The max daily pump efficiency is about 0.0017%. The SWHS could have max daily thermal efficiency of about 21%. It is concluded that the thermal efficiency was successfully improved, except for the pump one. The new SWHS with I m discharge head or lower is suitable for residential use. It adds less weight to a building roof and saves electrical energy for a circulation pump. It has lower cost compared to a domestic SWHS. (C) 2008 Elsevier Ltd. All rights reserved.