Blue roof design involves the detention of stormwater, which provides the opportunity to incorporate rainwater recycling and rainwater harvesting into the system. All that is required is for the water to be captured and then routed to cisterns, water tanks, or rain barrels.
While rainwater is harvested in most American states, it is severely restricted in Arizona, Colorado, Oklahoma, and Utah, all arid regions where water is a precious resource. Where water is mostly plentiful, harvested rainwater may be used for plumbing, for swimming pools, for gardens, for fire protection, even for consumption. In rural areas, it can be used for livestock.
New York State has even published a guide for harvesting rainwater that includes data relating to the amount of water that can be harvested legally. It also covers components of a rainwater harvesting system and discusses, in some detail, how to make rainwater safe for human consumption.
When a blue roof is used as a means to harvest rainwater, the catchment system must be designed with care. For instance, roofing material affects the quality of water and slope affects the quantity of runoff. A conventional roof that will feed rainwater into a tank would ideally be metal and have a reasonably steep slope. This won’t work with a flat blue roof design!
If you are considering harvesting rainwater from a blue roof, an experienced MEP engineer can advise on the best system for your building.