Alginate is the most widely materials used in dentistry. This impression material of alginate as a powder, will become hydrosol if mixed with water and then become hydrogel. Arrowroot starch has been studied to be a mixture of alginate. The good impression material should has enough time for setting. The aim of this research is to know the effect of water pH range towards the setting time of alginate impression material addition with arrowroot starch. The method of this research is experimental laboratories. There are 25 samples, that divided into 5 groups with different water pH range (3,pH 5,pH 7,pH 9,dan pH 11). The data analysis of this research using parametric One Way ANOVA. The result of this research show that the value of p<0,05 that means the water pH range has effect towards the setting time of alginate impression material addition with arrowroot starch. The conclusion of this research is the lower of water pH range, will make the setting time of alginate faster. The fastest of the setting time is water pH range at pH 3.