Applied Water Science, 2018; 8:77This paper examines efectiveness of groundwater governance structures and institutions in Mbarali District, Mbeya Region. The paper adopts exploratory sequential research design to collect quantitative and qualitative data. A random sample of 90 groundwater users with 50% women was involved in the survey. Descriptive statistics, Kruskal–Wallis H test and Mann– Whitney U test were used to compare the diferences in responses between groups, while qualitative data were subjected to content analysis. The results show that the Village Councils and Community Water Supply Organizations (COWSOs) were efective in governing groundwater. The results also show statistical signifcant diference on the overall extent of efectiveness of the Village Councils in governing groundwater between villages (P = 0.0001), yet there was no signifcant diference (P > 0.05) between male and female responses on the efectiveness of Village Councils, village water committees and COWSOs. The Mann–Whitney U test showed statistical signifcant diference between male and female responses on efectiveness of formal and informal institutions (P = 0.0001), such that informal institutions were efective relative to formal institutions. The Kruskal–Wallis H test also showed statistical signifcant diference (P ≤ 0.05) on the extent of efectiveness of formal institutions, norms and values between low, medium and high categories. The paper concludes that COWSOs were more efective in governing groundwater than other groundwater governance structures. Similarly, norms and values were more efective than formal institutions. The paper recommends sensitization and awareness creation on formal institutions so that they can infuence water users’ behaviour to govern groundwaterGroFutures project