Reusable Water Sources

With drought and dry conditions affecting much of the country, the idea of harvesting on-site water sources for non-potable reuse has increasingly become a part of sustainability conversations. Capturing and reusing rainwater, greywater, and even cooling condensate for non-potable uses like irrigation, toilet flushing, and cooling tower make-up makes a lot of sense in arid portions of the country where drought and water scarcity have always been a concern. However, the long-term sustainability of municipal water resources is a growing concern in many other parts of the country as well where fresh water resources seem abundant, and the idea of water harvesting may not be as common in those areas.

For this reason, Wahaso has created this helpful guide, highlighting our top five sources of harvestable water for on-site reuse.


Perhaps the most well-known of reusable water sources, rainwater has been captured and recycled for thousands of years. Rainwater is free and requires less treatment than other sources of reusable water, making it an ideal source for water harvesting. By definition, rainwater is precipitation that is collected from above ground surfaces, such as rooftops, which provides a generally clean source of reusable water, saving sanitization costs necessary for other sources of reusable water such as stormwater or greywater. For homeowners, simply investing in rain barrels can help reduce water usage, as collected water can then be reused to water plants. However, in commercial buildings, recycling rainwater can lead to sizeable water savings, as the large rooftop areas can often collect enough rainwater to meet most of the building’s toilet flushing and irrigation needs. For more information, visit our rainwater harvesting page.


While we may think of “rainwater” and “stormwater” as being synonymous, they are very different sources when considered for harvesting. Though they both come from the same rain event, “rainwater” is precipitation collected from relatively clean above ground surfaces, but once that rainwater reaches the ground, it becomes “stormwater.” Stormwater may be contaminated with silt, oil and fluids from cars, road salt, nitrates, and fertilizers from landscaped areas, and because of this, it requires additional filtration and cleaning steps. Despite that, once collected, filtered, and sanitized, stormwater is an excellent reusable source of water. Harvesting stormwater reduces pressure on the municipal treatment system, provides an onsite reusable source of water, and saves money and water by not having to use clean, municipal drinking water for irrigation or toilet flushing. For more information, visit our stormwater harvesting page.


Greywater- also known as graywater, grey water, or gray water- is differentiated from other reusable water sources as it has already been “gently used,” usually as water from showers and sinks. When properly cleaned and stored, greywater can be a valuable source of water to be reused for toilet flushing or for irrigation. An efficient greywater system requires a steady source of greywater from showers and sinks, so buildings with full time residents such as apartments, dormitories, hotels, and schools are excellent candidates for a greywater system. Because the supply in these buildings is steady and predictable and toilet flushing is generally linked to sink and shower usage, often the supply of greywater can meet 100% of the building’s toilet flushing needs. Although greywater requires additional sanitization and processing as compared to other reusable water sources, the storage requirements are drastically less than rainwater harvesting systems, which can bring the cost into the price range of a traditional rainwater harvesting system. For more information, visit our greywater harvesting page.


While cooling towers can be major consumers of water in a commercial building, they also produce significant amounts of potentially harvestable water as they dehumidify the air inside the building. Cooling systems in commercial buildings can generate over a million gallons of condensate each cooling season, yet this quality source of reusable water is often left unused and redirected into the municipal sewer system. As the amount of condensate produced by a cooling system is directly proportional to the load on the system, it is an efficient way to conserve and reuse water on-site. For more information, visit our condensate harvesting page.

Multiple Sources

Though not technically a source of reusable water, utilizing multiple sources such as rainwater, greywater, and condensate together can result in a highly efficient water recycling system as well as reduced municipal water usage, lessening the building’s impact on the environment. As rainwater is often an unreliable source of reusable water that fluctuates with the amount of precipitation, utilizing additional sources such as greywater and condensate that do not rely on precipitation is an excellent way to increase system efficiency. Each building has unique water supply and demand needs, so Wahaso evaluates all of a building’s available water sources and applications for reuse to minimize the use of municipal water. For more information, visit our multi-source system page.

Wahaso has designed over 800 water harvesting systems across the U.S. and Canada with over 25 years of experience in commercial and municipal systems. By incorporating a holistic approach in the design of our systems, Wahaso provides the optimal solution for your building, resulting in more sustainable and environmentally sound water use. For more information, contact us today.

About the Writer: Emily Avellana is a senior majoring in marketing at Elmhurst College and a Marketing Assistant at Wahaso.