The strength development and durability of concrete can be influenced by the quality of water used for curing the concrete. Consequently, this study was aimed at investigating the effect of contaminating the water for curing concrete on its compressive strength. Raw (tap) water and a water cement ratio of 0.6 were used in the production of the concrete cubes of 50 mm x 50 mm x 50 mm. The concrete samples produced were cured in raw water and water contaminated with varying percentages (25, 50 and 100%) of wastewater collected from a wastewater stabilisation pond. Chemical analysis was carried out to determine the pH, total dissolved solids (TDS), chloride, hardness, alkalinity, salinity, temperature and conductivity of the wastewater. The results of chemical analysis showed that these parameters are higher in the wastewater samples than in the raw water samples. The compressive strength of the concrete cubes were determined after 1, 3, 7, 14, 28, 60 and 90 days of curing. The compressive strength of concrete samples immersed in raw water, shows there was a progressive decrease in the strengths of the samples immersed in contaminated water as the percentage of the wastewater increased. Therefore, it is recommended that concrete that will be in contact with wastewater or sewage-polluted water should have been cured in uncontaminated water that gives assurance of maximum strength development. for the compressive strength of concrete cured in raw water, for 28 days the compressive strength of concrete in 25% waste H2O + 75% rawH2O, 50% waste H2O + 50% rawH2O and 100% wastewater content decrease by 12.35%, 25.44%, 35.74% respectively.