The integrity of a well is a crucial component for the longevity of a well. Cement isolates the casing and protects the well from fluids, pressure, and other components that may jeopardize its stability. Extreme care and research should be invested in analyzing the water quality that is used to mix cement. In this study, the effects of water quality on API Class G-Portland cement were studied to understand the relationship between water quality, rheology, thickening time, and compressive strength. Although extensive research has been made on well cement in general, no previous research focused on oilwell cement water quality was available until now. Thus, this paper is intended to serve as reference as well as motivation for future research. Cement thickening time was recorded using a cement consistometer and compressive strength using a universal testing machine. We tested several samples including soft to very hard, very saline and field waters. We also tested the hard water at different temperatures to investigate the effect of temperature on thickening time. A positive correlation occurred between the temperature of the mixing water and consistency, the higher the temperature was of the mixing water, the faster the consistency rose. In contrast, a negative correlation between water hardness and thickening time occurred. As water hardness increased, thickening time decreased and vice versa. A percentage change up to 2.4% was recorded between different water qualities making soft water (0 gm/L) have a longer thickening time in comparison to very hard water (180 gm/L+). Variations on the pH of the different waters used did not seem to have a significant impact on the results obtained. Compressive strength results showed that soft water (water with no hardness) is the strongest among the other samples prepared with different waters. In addition, a similar trend cannot be observed at different curing times. For instance, some samples show high strength on the first day but drops as cement hydration time increases.