ACTIVE APPROACHES FOR HARVESTING RAINWATER AND GREYWATER

By "actively harvesting” rainwater and greywater, we are referring to formal systems for collecting, filtering, storing and recycling water that would otherwise be sent to municipal sewer systems. Proper filtering and storage of harvested water are required to prevent the water from turning septic in storage – which could result in off-colors and odors. Local codes may or may not be in place that set standards for the required purity of stored water.

While these systems are more complex and more expensive than passive systems, they have the advantage of reducing the costs for municipal water and water treatment. It is considerably more expensive to retrofit these systems in existing buildings – particularly greywater systems that require separate internal plumbing. Rainwater systems can be more easily added if they are planned for irrigation or specialty uses, and there is adequate space available for the processing and storage systems.

A brief overview of active systems follows. For more information see Our Services

Active systems include the following Major components:

Collection: Rainwater is typically collected from building rooftops. We differentiate rainwater collected from parking lots and other impermeable surfaces as "stormwater" because it typically has more contaminants than rooftop rainwater. "Gently used" water collected from showers, sinks and washers is called "greywater." Water from toilets and kitchen sinks is termed "blackwater" and normally not included in water harvesting.

Pre-Filtering: Rooftop rainwater is relatively clean, but sill needs to be screened of leaves, gravel and other debris. This can be done by allowing the first few minutes of rain to flush the debris to the stormwater system. Screens and vortex filters can be used to more efficiently separate out larger debris particles. Prefiltering for dirtier water like greywater is sometimes done with settling tanks that allow heavy debris to sink to the bottom and floating debris to the top; a strainer floating below the surface pumps the cleaner water to the harvesting system. Strainer baskets in rainwater and greywater systems - similar to those used in swimming pools - can provide additional pre-screening.

Storage: There are many options for storing harvested water, and the best option depends on many factors - like the amount of supply and demand, the frequency of rainfall in the area and the availability of space to house or bury the tanks.

Tank sizes can range from a few hundred gallons to a half a million gallons or more and be made of polyethylene, fiberglass, concrete or steel, depending on their size and location in the building.

For more information on storage tanks, see our page on Storage Options for Harvested Water.

Sterilization: Water in storage must be treated with a sterilizing agent to keep the water clean. This can be by chemical addition of chlorine, chlorine dioxide, ozone, by recirculation past ultraviolet (U.V.) sterilizers or a combination of processes.

Final Filtration: A secondary filter removes remaining particulates in the water before it is stored, improving the water’s purity and clarity. This can be achieved with a sand filter or bag filter for most uses. When higher levels of purity are required -especially when harvesting greywater, ultra-filtration, reverse osmosis and carbon filters are also used. These can take the water quality to potable or near-potable purity.

Controls: Water harvesting systems in commercial and institutional buildings are held to a higher standard than residential buildings. These systems generally require a sophisticated control system that manages all aspects of the process.

These smart systems can determine when to add municipal water or divert excess water and waste to municipal sewer systems, the levels and purity of stored water, the status of filtration devices, etc. Sophisticated systems can interface with building automation systems for alarms and optimization.