Evaluating Rainwater Harvesting System for School Buildings

Freshwater is becoming limited as our climate and weather pattern changes. In this study, a rainwater harvesting system was evaluated for collecting and utilizing rainwater for uses in non-potable purposes. Water-Balance was carried out for two design scenarios: Single tank and double tank, for irrigation in all main fields (202,724 ft²). The irrigation demand for the entire field was estimated to be about 1.08 million gallons on average after analyzing 14 years of data (2000-13). Installing a single tank of 210,000 gallon capacity was found to reduce the demand by 23%, whereas double tank installation was found to reduce the demand by about 10% on an annual basis. For these demand, irrigation needs has to depend on other sources such as city water supply or school’s retention pond. The cost-benefit analysis revealed that the system will have estimated initial cost of $85,000 (single tank installation). The corresponding annualized cost of ownership is $5,215 while projected savings on annual water bills is $6,079. The system could be paid off early, resulting in savings of about $45,000 for the life of the system. The system was found to benefit financially while contributing to the environment by conserving the freshwater from non-potable use and reducing hydrologic footprint by harvesting the stormwater runoff.