Renewable Sources For Water Harvesting

Renewable Sources For Water Harvesting

There are a number of water sources that can be harvested for reuse: Rainwater, Stormwater, Greywater, Groundwater and Condensate. Each has its own set of advantages and disadvantages as well as implications for capturing, cleaning, storage and use.



Rainwater collection and storage, (also known as “rainwater catchment”), has been practiced for centuries by cultures throughout the world. Even in the U.S., most 19th century and early 20th century homes had cisterns that saved rainwater from rooftops to use for washing clothes and watering gardens. In industrial countries, the practice had largely died away with the introduction of reliable modern water supply systems. This trend is now changing.

What is rainwater?
“Rainwater” by definition is precipitation that is collected from relatively clean, above-ground surfaces – usually rooftops. Because rooftop rainwater has minimal contamination, it is an ideal source for harvesting. In commercial buildings, the large rooftop areas can often collect enough rainwater to meet all the non-potable uses such as toilet flushing and irrigation. For more information on how Wahaso treats rainwater, visit our Rainwater Harvesting Systems page. Rainwater is free, mostly clean and requires less treatment than greywater, so it is an ideal source of water for harvesting.


An efficient greywater system first requires a steady source of greywater. The most abundant source is showers in buildings with full time residents – apartments, dormitories, hotels, schools, etc. Some manufacturing facilities can harvest water used in their manufacturing processes if it is not heavily loaded with contaminants.

What is greywater?

Greywater, (also called grey water, graywater and gray water) refers to water that has been “gently used” in sinks, showers, baths and light industrial applications and has not yet been treated. It is clearly distinguished from water from toilets, referred to as “black water”. Properly filtered and stored, greywater can be a valuable source of water to flush toilets and urinals or irrigate landscaping. Toilet flushes can account for 25-65% or more of the total water use in a commercial building, even when low-flush fixtures are used.

Office buildings generally do not produce enough usable greywater to warrant the cost of a system. When there is an abundant supply of greywater, it can be a more reliable source of water for flushing toilets than rainwater. The amount of shower and sink usage generally ties to the amount of toilet use in a building, so there is almost always a balance in supply and demand for greywater.

There are significant implications for the use of greywater. Greywater harvesting requires additional treatment versus rainwater and is always an active system versus a passive if it is to be used inside a building or for spray irrigation. The additional filtering and sterilization requirements increase the cost of a system vs. rainwater harvesting systems. However, because daily supply and demand are in balance with a greywater system, the cost of storage tanks for a greywater harvesting system can be significantly lower than for a rainwater harvesting system, bringing the total system cost into the price range of a large rainwater system.

As a relatively new form of water conservation, many communities have not yet set standards for greywater processing and storing. Local codes often restrict the use and storage of greywater but the codes are meant to protect public safety from the contaminants in untreated greywater. Once the greywater has been treated, its definition becomes “onsite treated non-potable water” and falls under a different set of usage and storage guidelines. Water Harvesting Solutions has extensive experience in developing greywater systems for commercial properties. Our greywater system has third-party certification for both IAPMO 324 and NSF/ANSI 350. Read more about Greywater Harvesting Systems.



Many municipalities are now requiring new buildings to include plans to collect and manage this stormwater runoff so that it does not contribute to overloaded municipal systems. Property owners can spend hundreds of thousands of dollars to filter and detain stormwater and then release it slowly back to the local municipality. Ironically, these same property owners then buy back municipal drinking water to flush toilets and irrigate their landscaping!

What is stormwater?

“Stormwater” is defined as precipitation collected off outdoor ground level surfaces. This water may be contaminated by automobile oils and fluids, unknown chemical spills, and nitrates or pesticides that run off from landscaping. In commercial buildings, it is usually the parking lots that throw off vast amounts of stormwater during a rain event, which can be millions of gallons per year. Unmanaged, stormwater can run off into streams and rivers with its contaminants. At the very least, it must be conveyed miles away for treatment in a municipal stormwater system using energy and resources.

Wahaso can provide a system to clean, store and apply this vital water resource. Integrated cistern systems can prefilter the stormwater organically before it is stored, significantly reducing the filtration required in the active harvesting system. For more information on how Wahaso treats stormwater, visit our Stormwater Harvesting Systems page.



While cooling towers can be major consumers of water in a commercial building, they can also produce significant amounts of harvestable water as they dehumidify the air inside the building at the cooling coils. In larger buildings, this clean source of water can generate a million gallons or more in a cooling season!
What is condensate?

While cooling towers can be major consumers of water in a commercial building, they can also produce significant amounts of harvestable water as they dehumidify the air inside the building at the cooling coils. In larger buildings, this clean source of water can generate a million gallons or more in a cooling season! Even buildings with this much condensate supply do not need a large or expensive system to treat and reuse the water. If using the water for cooling tower make-up, the turn-over of the harvested water is quick and therefore the system does not require large tanks. Wahaso’s condensate system has a compact design that fits easily into existing and new buildings Learn more about our Condensate Systems.



If your building will have a basement or parking area below ground level, then a sump system will likely be planned to remove groundwater from around and under the sub-ground areas. Traditionally, groundwater is discharged into the municipal sewer or stormwater system, wasting its potential and further burdening the municipal system – a lost opportunity!
What is groundwater?
Groundwater can be the clean source of water for non-potable applications but depending on the site, may also contain harmful contaminants. Wahaso recommends testing to determine if any what, if any, contaminants are present.

Which sources of on-site water are best to collect for your location? That “depends” on so many factors. Wahaso provides a free, no-obligation water balance and report that can quantify potential sources and match them with an appropriate harvesting system.

Please Contact Us and we can begin an analysis for your project.

Since 2004

Wahaso Mission

Our mission at Wahaso is to help municipalities and commercial property owners reduce the impact of their buildings on the environment through innovative and sustainable water practices.