Many communities have tightened requirements for the handling of stormwater from commercial buildings. Impervious surfaces on roofs and large parking areas add to overloaded water treatment facilities. During heavy rains, the facilities can become overwhelmed resulting in raw sewage being dumped into open waterways. Not a good thing!

Stress on municipal storm systems can be reduced with water harvesting. The many methods of harvesting rainwater or greywater can be categorized into two main groups: Active and Passive. Which is best for your building depends on a number of factors including the amount of rainfall received in your geography, the square footage of the building roof and parking areas, the value of collecting the water and using it in a directed way, etc. Water Harvesting Solutions may suggest a combination of passive and active systems depending on your unique situation and requirements.


Building owners can help reduce the impact of stormwater runoff, even if there is no plan to reuse the water. A “passive” water harvesting system means that there are no mechanical methods of collecting, cleaning and storing rainwater. The intent with passive rainwater management is to create areas to contain waters until they can naturally be absorbed into the land. Vegetative swales, wetland ponds, dry creek beds, green roofs and pervious concrete or pavers are some examples used to keep the water on the land longer and out of sewer or stormwater systems.

These methods are relatively simple and inexpensive and require only that building and landscape designers keep a “green eye” during the planning process. It is common to incorporate both passive and active approaches when handling rainwater and stormwater, optimizing the application of each method. Read more about rainwater and stormwater harvesting.

Water Harvesting System

Green Roofs

Green Roofs

Vegetated Swales

Vegetated Swales

Detention Ponds

Detention ponds are a long-used method of stormwater management. During a storm event, the water is directed to a pond on the property, where it can be stored. The benefit of this passive harvesting method is that it can be a pleasant feature to overall landscape design. It can also create an environment that
supports local wildlife.
However, the biggest disadvantage of detention ponds is that they utilize valuable real estate to hold stormwater and may create problems with insects, odors and public safety.


Active water harvesting refers to formal systems for collecting, storing,and treating water that would otherwise be sent to municipal sewer systems. Proper storage, filtration and sanitation are required to ensure that the water is suitable for reuse.

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 if there is adequate space available for the processing and storage systems.

Wahaso specializes in many methods of active water harvesting:

  • Rainwater harvesting systems: Our sophisticated systems filter, sanitize and store collected rainwater to produce high-quality water that meets strict water quality codes for commercial and institutional buildings. Rainwater is collected from impermeable rooftops and reused in toilet flushing, irrigation and other non-potable applications.
  • Greywater harvesting systems: Greywater (also referred to as grey water, gray water and graywater) harvesting systems utilize “gently used” water collected from showers and lavatory sinks. Greywater harvesting in commercial residential buildings provides a more constant water supply than a rainwater system due to the seasonal and regional nature of rainfall. However, greywater also contains a higher level of biological and chemical contaminants, which requires a more rigorous filtration and sanitation process. Wahaso’s greywater system is IAPMO 324 certified and is currently undergoing testing for NSF/ANSI 350 certification at the IAPMO R&T Lab.
  • Stormwater harvesting systems: Stormwater is defined as rainwater that has reached the ground. It is water from parking areas and landscapes that is more likely to be contaminated with silt, hydrocarbons from automobiles, road salt in northern climates, nitrates, other fertilizers from landscaped areas and more. While stormwater can be more contaminated that rooftop rainwater, the Wahaso system offers robust filtration and sanitation and is
    IAPMO 324 certified.
  • Condensate harvesting systems: Many commercial buildings have air handling units that generate condensate during on warm, humid days. Harvesting this source for reuse can be relatively inexpensive and efficient if the water can be directed to a single point for treatment. Wahaso’s condensate systems filter and sanitize the water, and are designed to fit easily in both new and existing buildings.
  • Multi-source harvesting systems: In many cases, the most efficient way to meet the water needs of a particular building is to combine the capabilities of multiple harvesting systems. For instance, we may be able to maximize water savings by capturing both rainwater and condensate and using the harvested water to flush toilets and irrigate the landscaping of a facility. Our multi-source, multi-use harvesting systems are custom designed to utilize water from all possible sources and apply treated water to all possible uses.

To determine the most efficient sources and uses of water and to develop a system concept that will deliver on that savings, contact Wahaso for a free consultation.

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