| There is a fast-growing interest in capturing and | | | | micron range. |
| reusing rainwater in commercial buildings to reduce | | | | Storage: There are many options for storing |
| costs for municipal water and also to reduce the | | | | harvested water, and the best option depends on |
| impact that a building has on the surrounding | | | | many factors - like the amount of supply and |
| environment and on the municipal sewer and | | | | demand, the frequency of rainfall in the area and |
| stormwater systems. Rainwater from rooftops | | | | the availability of space to house or bury the |
| can be captured or "harvested" and used to | | | | tanks. |
| replace municipal drinking water for many | | | | Tank sizes can range from a few hundred gallons |
| non-potable applications. Rainwater harvesting can | | | | to a half a million gallons or more and be made of |
| be categorized as either "active" or "passive". This | | | | polyethylene, fibreglass, concrete or steel, |
| article will help the reader understand the major | | | | depending on their size and location in the building. |
| components of active commercial rainwater | | | | For more information on storage tanks, see |
| harvesting systems. | | | | Storage Options for Harvested Water |
| By "actively" harvesting rainwater, we are | | | | Sanitation: Most commercial rainwater harvesting |
| referring to formal systems for collecting, filtering, | | | | systems include one or more processes that |
| storing and recycling water that would otherwise | | | | sanitize the water to kill bacteria, viruses and |
| be sent to municipal sewer or stormwater | | | | other pathogens. This stabilizes water being |
| systems. These are differentiated from passive | | | | stored for long periods of time, and ensures public |
| harvesting systems that usually detain rainwater | | | | safety of water the will be brought into the |
| in vegetated swales so that it can infiltrate | | | | building or sprayed on landscaping around the |
| naturally back into the soil. | | | | building. |
| While active systems are more complex and | | | | There are many approaches to sanitation, which |
| more expensive than passive systems, they have | | | | can include the addition of chlorine, chlorine dioxide, |
| the ability to significantly reduce the costs for | | | | ozone, or by circulating the water past ultraviolet |
| municipal water and water treatment- especially in | | | | (U.V.) sterilizers. Ultraviolet sterilization is ideal for |
| commercial buildings with large rooftops and | | | | water being applied for irrigation because it is |
| concentrated numbers of occupants. A | | | | chemical-free and very low maintenance. When |
| commercial building that captures all of its rooftop | | | | the water is used inside the building – usually |
| rainwater for harvesting can often save 1-2 million | | | | to flush toilets – most municipalities require |
| gallons of municipal drinking water per year. | | | | adding chlorine as the disinfectant so that there is |
| These systems are most efficient when designed | | | | a measurable "residual" level of pathogen-killing |
| into the mechanicals of a new building so that | | | | capability. |
| capture, treatment and application of the | | | | Final Filtration ("Polishing"): A final filtration step is |
| harvested water are integrated into the rest of | | | | usually included in commercial systems to remove |
| the building – particularly when the harvested | | | | remaining particulates in the water before it is |
| rainwater is used to flush toilets in the building. To | | | | applied; this step improves the water's purity and |
| flush toilets with harvested rainwater, separate | | | | clarity, "polishing" it for final use. This can be |
| non-potable water lines must be run to each toilet | | | | achieved with a mechanical filter using a fine |
| in the building; this can be prohibitively expensive in | | | | micron screen, sand filters or bag filters. When |
| a large existing building. Systems can be | | | | higher levels of purity are required -especially |
| economically retrofitted into existing buildings, | | | | when harvesting greywater, ultra-filtration, |
| however – especially if the harvested | | | | reverse osmosis and carbon filters are also used. |
| rainwater is used for irrigation of landscaping or | | | | These can take the water quality to potable or |
| for cooling tower. | | | | near-potable purity. |
| Systems in commercial buildings that process | | | | Controls: Water harvesting systems in commercial |
| millions of gallons of harvested rainwater per year | | | | and institutional buildings are held to a higher |
| require proper engineering design and | | | | standard than residential buildings. These systems |
| commercial-grade components to meet higher | | | | generally require a sophisticated control system |
| standards of treated water safety and reliability. | | | | that manages all aspects of the process. |
| Active systems generally include the following | | | | These smart systems can determine when to |
| major components: | | | | add municipal water or divert excess water and |
| Collection: Rainwater is typically collected from | | | | waste to municipal sewer systems, the levels and |
| building rooftops. Rainwater collected from parking | | | | purity of stored water, the status of filtration |
| lots and other impermeable surfaces is termed | | | | devices, etc. Sophisticated systems can interface |
| "stormwater" and is treated differently than | | | | with building automation systems for alarms and |
| rainwater because it typically has more | | | | optimization. |
| contaminants than water collected from relatively | | | | The cost for commercial rainwater harvesting |
| clean rooftop surfaces. "Gently used" water | | | | systems is directly related to the amount of |
| collected from showers, sinks and washers is | | | | water captured and stored and applied. Areas |
| called "greywater" and requires more complex | | | | with regular monthly rainwater events require less |
| treatment. Water from toilets and kitchen sinks is | | | | expensive systems due to reduced storage |
| termed "blackwater" and normally not included in | | | | capacity requirements. System costs generally |
| water harvesting systems. | | | | range from $25 – 100K including engineering |
| Pre-Filtering: Rooftop rainwater is relatively clean, | | | | design and installation support. System payout is |
| but still needs to be screened of leaves, gravel | | | | directly related to the costs for municipal water |
| and other debris. This can be done with a "first | | | | replaced by the system – and can range from |
| flush" system that sends the first few minutes of | | | | 6-12 years. Wahaso – Water Harvesting |
| rain to flush the debris to the stormwater | | | | Solutions, Inc. provides full design-build support; |
| system. More efficient systems screen the water | | | | initial system scoping is provided at no cost by |
| mechanically – or use a vortex action to | | | | the company. |
| separate out larger debris particles in the 200+ | | | | |