The corrosion behaviour of plain-carbon steels in water environments has been studied. In this study, a wide range of carbon steels are used in the most common corrosion environments which are salt water and drinking water. The specimens were immersed in the water media and corrosion rates evaluated, using the weight loss method. The effect of carbon content, corrosion environments and time of immersing on the specimens corrosion rates of Hypo-eutectoid plain carbon steels have been studied. The aim of this work is to study the effect of carbon content on the corrosion rate of carbon steels in different corrosion media and various time intervals. The obtained results showed that there is a clear correlation with the microstructure where higher Pearlite show higher corrosion rate, so the corrosion rate increases with the carbon content. The results also show that the corrosion rate of carbon-steel in salt water is higher than its value in drinking water. It is also found that longer exposure time, leads to a lower corrosion rate while weight loss is still increasing.