Abstract. Concrete is a porous material, and its longevity is primarily determined by the passage of water through it. As a result, this research discusses the influence of fly ash on concrete water absorption. Cement was replaced with four different amounts of Class F fly ash: 30%, 40%, 50%, and 60%. The samples were cured for 3 days at 20°C and 95% relative humidity (RH) before being tested for their water absorption properties. It was found that the samples containing more than 40% fly ash had lower water absorption rates than those containing less than 40% fly ash. Conclusion: Fly ash has an inhibitory effect on concrete water absorption. Replacing cement with increasing amounts of fly ash decreases the concrete's water absorption capacity. This may be due to the fact that cement is the main source of hydrophilic particles in concrete, while fly ash is hydrophobic. However, more research needs to be done on this topic before any final conclusions can be made.