Two identical solar water heaters (solar panels) have been built and installed at the Agricultural and Veterinary Research Station of King Faisal University in order to study the effect of water column length passing through the solar panel on its thermal performance. Each solar panel having a surface area of 2 m² (2 x 1 m) with different number of copper pipes (but they had the same total length of 20 m). Operating liquid (water) was continually cycled through the solar panels using natural and forced systems of circulation. After passing through solar panel, the heated water was stored in an insulated storage tank (300 litres). The daily average overall thermal efficiencies during this experimental work for the short and long pipes of solar panels were 71.73% and  61.13% respectively. Consequently, the solar panel with short pipes was found to be more efficient than the solar panel with long pipes by  17.29%.