Solar energy is becoming an alternative for the limited fossil fuel resources. One of the simplest and most direct applications of this energy is the conversion of solar radiation into heat, which can be used in water heating systems. A commonly used solar collector is the flat-plate. Actually a lot of research has been conducted in order to analyze the flat -plate operation and improve its efficiency. Solar water heating is a process of tapping energy from the sun for the purpose of raising the temperature of water from local water supply to some desirable higher temperature. This paper discusses improving the performance of a liquid flat plate solar energy collector (which is thermosyphon flat plate collector) integrating with external reflectors. The external flat reflectors are mounted on the side of the collector. The external flat reflectors can be tilted to an angle of 15°, 30o and 45°, on the horizontal plane due to the existence of angle adjustment. The effect of four flat plate reflectors which are mounted on (bottom, top, left, and right side reflectors) on the total light radiation on a collector at tilted plane angle of 45o for each reflector is analyzed The effect of these reflectors is more evenly at solar noon since the sun is perpendicular to the collector. Based on this the effect of the reflectors on the collector are analyzed. The flat plate collector integrated with and without reflector for minimum, average and maximum solar radiation intensity of bahir dar has been analyzed, constructed and tested on automotive work shop at bahir dar institute of technology. Experimentations are conducted on flat plate collector with and without reflectors for particular period of various days and data is collected /maintained as per days. For flat plate with reflector the maximum fluid output temperature, and insolation of 98°C, and 1,200 W/m2, respectively, was obtained on a sunny day. Whereas for flat plate without reflector the maximum temperature and solar insolation is 70oc and 1,200 W/m2, respectively, was obtained on a sunny day. The total thermal energy generated by thermal collector with reflectors in optimal position is significantly higher than total thermal energy generated by thermal collector without reflectors. This solar water heating system finds useful application for cooking, pre-heater when temperature of more than 70oC is needed, and for bleaching industrial process in textile factory. The theoretically and experimental results of water outlet temperature are equivalent with the results obtained by using computational fluid dynamics CFD fluid flow (CFX) and there is a good agreement in between them.