Given that Iran will face a water crisis in the coming decades, more attention has been paid to resolve the problem. Today, the use of concretes with low permeability in many offshore structures has been the subject of interest for design engineers. In water conveyance canals, which are mainly made of concrete, water losses occur through surface and deep cracks. In addition, leakage of water through cracks in the concrete can cause problems such as freezing, consecutive moistening and drying, chemical attacks (if any) and thereby, the failure of the concrete and the loss of financial resources. The use of grout to repair cracks is one of the most effective ways to control leakage in water conveyance canals, because both economically and environmentally it is more appropriate than other methods. The present thesis was performed in two parts. In the first part, various tests were conducted to determine the most effective grout to reduce the amount of water leakage through concrete specimens. To choose the best mix design, various admixtures such as bentonite, silica fume and nano silica, mix designs were added. The parameters considered in this study were the ratio of W/C, and weight percentage of Bentonite, silica fume and nano silica. The effect of these parameters on compressive strengths of 7, 28 and 90 days, flowability and bleeding and expansion of grouts were investigated. Results showed that by increasing the value of W/C, the compressive strength of specimens reduces, while the flowability and bleeding of specimens increase. Increase of bentonite in the mix containing bentonite only has a slight reduction on the compressive strength at early age, improving as the age increases. The combination of bentonite with silica fume or nano silica increases considerably the compressive strength and reduces bleeding of the grout. Among them, silica fume has the greatest impact on reduction of grout bleeding. After reviewing the results of various tests, three designs were selected as the optimal mix designs. In the second part, methods for repairing cracks in the concrete samples to reduce water leakage were investigated. To create artificial cracks in the specimens, Brazilian tensile test were used. Based on previous findings, three cracks with widths of 100, 200, and 400 microns were considered. Cracks were repaired by two methods; i.e., manual injection and pressure injection. Permeability tests with pressure of 0.2 and 5 bars were performed to measure the amount of water leakage, using concrete permeability apparatus. In the present work, the amount of water leaking from the cracks was measured instead of the penetrated depth of water inside the sample. The water Leakage of the concrete specimens before and after crack repairs was measured. The results showed that repairing the cracks with grout reduces the leakage and cracks with more width gives better results; i.e., the greater the width, the le the leakage. With pressure injection, less water leakage occurs. Mix design contains silica fume and 1% bentonite was selected as the best mix design to reduce the water leakage. Key words : Grout, Bentonite, Silica fume, Nano silica, Water Canal, Leakage of water