As per LEED requirements in this credit, up to X percentile rainfall events should be retained on-site, through infiltration, evapotranspiration and reuse, and must not be discharged into surface waters.
Our project is in Shanghai, a previous developed unban site. It is mainly for commerical use, and few infiltration methods can be adopted. Rainwater is proposed to be harvested in cisterns, and reused for toilet flushing, irrigation, roads cleaning, cars washing, etc. However, harvested rainwater is quite large in ammount (aprox. 1000m3 according to 90% percentile), and daily consumption is relatively small (aprox. 100m3). So if 90% percentile rainfall happens, it will spend 10 days to comsume the harvested rainwater.
My question is if there are several consecutive rainy days, we may have overflow to our cisterns and this amount of water can only be discharged rather than retained onsite for future uses. When this happens, will we still meet the LEED requirement? How is the overflow usually handled in such case?
Any comment is appreciated. Thanks in advance.