Evacuated tube solar water heater is one of the high performance solar systems. As its disadvantages, it is vulnerable to pressure of piping system and it may be susceptible to forming stagnant region at the end of each tube. In this region low temperature and declining of natural convection result in collector's efficiency drop. By introducing an improved solar water heater the mentioned disadvantages have been removed and a prototype was built and examined. The experiments were divided into two phases, i.e. energy absorbing and energy harvesting phases. The experiments of energy absorbing phase included improving the entrance of evacuated tubes, renovation of fluid motion path in different tilt angles, optimum distance of reflector and using SiO 2 -distilled water nano-fluid as circulating fluid. Also, the experiments of energy harvesting phase included, using nano-fluid as circulating fluid and studying the effect of mass flow rate of consumable water on the system performance. Without the entrance renovation, the system showed almost the same performance for different slopes; however the total absorbed solar radiation were different. Since stagnant region does not form in renovated system, with increasing the tilt angle the efficiency increased and the most efficiency enhancement was achieved for tilt angle of 75 o as much as 30%. Using the reflector made the total absorbed solar energy to increase via capturing the escaping radiations passing through gaps between tubes. According to experiments, by increasing the distance ratio from zero to 1.3, the efficiency went up and afterward it remained almost constant. So that the distance ratio of 1.3 reported as the optimum distance ratio for reflectors in which the efficiency of solar water heater increased by around 16% comparing to similar solar water heater not benefiting the reflector. The experiments corresponding to investigating the impact of nano-fluid on performance of solar water heater were carried out for four mass concentrations of 0.07, 0.15, 0.3 and 0.45%. According to results using nano-fluid as circulating fluid also caused the performance of solar water heater to improve and maximum efficiency enhancement was achieved as much as 4% for 0.15% mass concentration of nano-fluid particles. As conducted through energy harvesting phase, the total gained exergy showed very marginal variations and the highest second law efficiency was achieved for flow rate of 0.8 . Eventually the experiments regarding energy harvesting for different mass concentration of nano-fluid were carried out and the highest second law efficiency enhancement as much as 9% was achieved for mass concentration of 0.15%. Keywords: Solar water heater, Water in glass evacuated tube, Nano-fluid, Reflector, Mass flow rate changes.