Rainwater harvesting from roof is considered as valuable water resources. Material Flow Analysis (MFA) of water in Mahasarakham University (Khamriang Campus) shows that rainwater harvesting from roof can reduce water supply production by 7% and save more than 200,000 Bt/year for water treatment cost. The sensitivity analysis suggests that by 5% water supply conservation and 20% additional rainwater harvesting, MSU could have enough water resources. The rainwater is suitable to be substituted water for gardening due to the convenience to assemble an above ground storage tank or a pond to store harvested rainwater from roof. The current practice of rainwater is collected and discharged into drainage system and treated in wastewater treatment plant. Utilisation of rainwater harvested could reduce wastewater amount that must be treated by 9%. Rainwater harvesting and reuse should be promoted in campus in order to encourage sustainable living and water conservation policy.