This measure can be claimed if a rainwater collection system is installed to supply water for use within the project. This water must be re-used on the project site to replace water consumption from the municipal water supply. End uses may include flushing toilets, the HVAC system, cleaning the building, or irrigation of landscaping.
A rainwater harvesting system can reduce the use of fresh water from the municipal supply.
To qualify, the collected rainwater must be re-used on the project site, and demonstrate that it replaces municipal water supply. The project team must document both the need for municipal water supply for the enduse being served, and the fact that the collected rainwater is being directed to replace it. For example, the team could submit pictures that show the planned piping system connected to an irrigation system. This would ensure that the system is reducing municipal water use.
EDGE automatically calculates the approximate maximum quantity of water that can be collected by a rainwater harvesting system using rainfall data from the project location and the size of the roof area. Although the default assumption is that the roof will serve as the rainwater collection system, a rainwater collection system located on the grounds of the project is just as acceptable provided it is properly sized.
Detailed guidance for sizing a rainwater collection system is available on the worldwide web and would normally be carried out by the supplier of the system. However, the following can be used as a rough guide:
Catchment Area = area of rooftop or hardscape (m²).
Rainfall volume = average annual rainfall (mm), also called “amount potential”
Run-off coefficient = varies depending on the surface type. some examples are as follows: Metal roof - 0.95, Concrete/asphalt roof - 0.90, Gravel roof - 0.80
If hardscape is included, it can also be expressed as a percentage of the roof area. For example, if a building has a 1000 m2 roof and another 500 m2 serving as rainwater catchment area, the EDGE input for % of Roof Area used can be 150%.
The main consideration when designing a rainwater harvesting system is adequate sizing of the storage tank. The supplier/designer of the system must be able to advise on appropriate sizing, but the two key factors to consider when sizing the tank are the rate of supply (local rainfall data and collection area) and the demand (water use per day).
When harvesting the rain water, a dual piping system must be used to separate the rain water from the mains and to distribute the collected water for use at the project site (such as flushing toilets, the washing machine or showers).
Collected water must be in accordance with local or international health and sanitary code requirements (whichever are more stringent).
Relationship to Other Measures
Claiming this measure reduces the water demand for all uses considered by EDGE.
The base case assumption is that no rainwater is harvested. The improved case assumes that the rainwater harvesting system is adequately sized and that the rainwater collected is used internally for such purposes as flushing toilets and showers. When this measure is claimed, dual piping is required to avoid cross-contamination of water.
|Design Stage||Post-Construction Stage|
At the design stage, the following must be used to demonstrate compliance:
At the post-construction stage, the following must be used to demonstrate compliance:
EDGE assumes that the rainwater is being used within the building. If the rainwater is being used only to irrigate the landscape, the project team must demonstrate that (1) there is need for irrigation with municipal water (in addition to just natural rainwater) and (2) that the recycled water will be directed to this use. This can be done with drawings of the plumbing layout at the design stage, and with pictures that show the planned piping system connected to the irrigation system at the post-construction stage.
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