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.