A solar distillation system has been designed and installed in NCSR "Demokritos". The system consists of three parts: an asymmetric, single-effect solar still of greenhouse type, integrated storage and a flat-plate collectors field. The thermal behavior of the system was investigated by two series of test, first in the solar still unit only and second in the solar still coupled with a storage tank, heated by a solar collector field. The influence of coupling the solar still with a hot water tank is reported, especially concerning distilled water productivity. It was found that coupling a solar still with a hot water tank generally doubles the distilled water output in the 24-h period, as a result of continuous heating of basin water from tank water. Increases are higher at night than in the day, since at night differences in water and cover temperatures are generally higher, resulting in higher production rates. The hybrid design of this system, apart from being able to supply desalted water together with hot water, leads to significantly higher water productivity in the day and night. Moreover, it can use available heat such as waste heat, coming from thermal processes nearby, optimizing exploitability of any available heat sources.