The influence of different irrigation water amounts was evaluated on tomato cultivation in the field experiment conducted in greenhouse, in Tokyo University of Agriculture, Japan, to determine the optimal water use amounts for dry season agriculture for vegetable cultivation in Uganda. The field was divided into three blocks (A, B and C) and soil samples were taken from each block for laboratory analysis. Hydraulic discharge measurement of low pressure drip irrigations system was carried out to assess the application efficiency of emitter discharge due to varying pressure distribution. Different irrigation water amounts (2 mm, 3 mm and 4 mm) were applied to blocks A, B and C respectively after 14 days of transplanting and tensiometers were installed to monitor the matrix potential at 10 cm soil depth. The results showed that the difference in emitter discharge was nearly constant due to small pressure distance of 5 m that corresponds to the field length. From statistical analysis, application of 4 mm and 3 mm irrigation water amounts had no significant difference on tomato growth, although 2 mm affects growth which could lead to wilting. Therefore, we can help smallholder farmers in Uganda, to optimize and save irrigation water use during dry and moisture deficit seasons, without affecting the crop growth and yield by application of 3 mm/day.