The term “wastewater” is a misnomer.
In fact, wastewater is made up of distinct and valuable resources: nutrients, water, and energy. Each of these resources is recoverable and ripe for reuse.
According to the United Nations Environment Programme, only 11% of wastewater produced globally is currently being reused. The untapped potential for reuse is around 84.5 trillion gallons (320 billion m3) per year, with the ability to supply more than 10 times the current global desalination capacity.
The industry now recognizes that failing to recover these resources is a lost opportunity. The European Commission estimates that the EU could reuse six times more treated water than it currently does. The world is urbanizing and, in many places, growing populations are straining existing water and sewer infrastructure, much of which was constructed decades ago. New York City, Mexico City, Cape Town, Mumbai, Chicago, London and others have all seen consequences of water and sewer infrastructure that is over a century old.
In the United States, multiple cities already require or incentivize onsite reuse systems for new construction. San Francisco requires blackwater systems for new commercial buildings and greywater systems for new multifamily buildings exceeding 100,000 square feet. Austin requires rainwater and condensate reuse systems for most new construction. Florida offers a density bonus to developers to build more units if greywater recycling is implemented. And more cities are following suit. In Europe, regulations such as Regulation (EU) 2020/741 and the Circular Economy Action Plan address the need for decentralized, circular systems.
The key to the success of these regions’ approach? Take the burden off municipal systems by recycling wastewater in the building itself. And in the process, provide water savings and lower utility costs.
How technology can help ease water woes
Onsite water reuse, also known as decentralized water recycling, is a process that captures wastewater at the building scale, treats it using equipment within the building, and returns it for reuse within that same building. This closed-loop system allows the same volume of water to be reused multiple times within the building, saving a project 50-95% of its municipal water intake.
There are multiple source water options for a project to choose from. Rainwater systems capture rain that falls onto rooftops. Stormwater systems capture rain that falls onto hardscapes at grade. Condensate systems collect water from air conditioning systems, refrigeration units, and steam production. Greywater systems capture wastewater from plumbing fixtures that don’t have human or animal waste products, and blackwater systems capture all plumbing fixtures.
The applicability of onsite reuse systems is vast because there’s such a range of possible system types. The rainwater barrels that irrigate a homeowner’s garden and the blackwater system recycling 30,000 gallons every day at Salesforce Tower are both examples of onsite reuse, just at different scales.
There’s also a wide range of applicable uses for recycled water. Currently, most onsite reuse systems treat water for non-potable applications such as toilet flushing, irrigation, cooling tower makeup, and laundry. In commercial buildings, regulations allow for up to 95% of water use; in residential buildings, up to 50%.
That’s just the water piece.
Onsite reuse systems can also recover energy through wastewater heat recovery. The beauty of wastewater heat recovery is in its simplicity. Wastewater heat is present in any building that uses hot water fixtures: sinks, clothes washers, showers. That thermal energy can be stored within the wastewater collection tank and recovered using heat exchangers or heat pumps, making wastewater a low-impact and “renewable” source of heat.
Wastewater heat recovery is already common in Europe and is now gaining traction in the U.S. It's estimated that recovering heat from wastewater in all U.S. residential and commercial buildings could save up to 350 billion kilowatt-hours of energy each year, equivalent to the annual energy use of over 30 million homes.
Solids recovery is another potential benefit of onsite reuse. The solids in blackwater systems can be filtered out, dewatered, and processed into usable soil amendments that can be used in fertilizer, soil mixes, and many other applications. Several utility companies — including DC Water, Milwaukee Metropolitan Sewerage District, Philadelphia Water Department, Thomas P. Smith Water Reclamation Facility in Tallahassee, and more — are transforming blackwater into soil amendments through the production of biosolids. Decentralized treatment systems are enabling projects to utilize wastewater resources for reuse onsite in landscape beautification.
Projects that benefit from onsite reuse systems
Onsite reuse can be designed and installed for any project in any location. In general, larger systems show better payback by being able to reuse and offset the most potable water and sewer utility costs. Onsite reuse is beneficial in any of the following project circumstances:
- The project wishes to become more self-sufficient, resilient, or off-grid.
- The project site has no connection to the municipal sewer. In this case, the project site must treat and dispose of all its wastewater, and by reusing as much as possible, will save water and reduce dispersal requirements.
- The project is located in a dense urban area with high water and sewer rates. Reusing water onsite will save on utility costs; in many instances, the payback period of onsite technology is less than 10 years.
- Goals include sustainability and resilience targets or achievements such as LEED, Living Building Challenge, or Net-Zero Water; the project’s target tenants value sustainability and green living.
- Municipal recycled water is either not available or is not the best option financially.
The project has a large volume of rainwater or stormwater supply. This type of reuse system typically has fewer treatment and maintenance requirements than more comprehensive systems like greywater or blackwater. Rainwater systems are relatively simple systems that can still provide high water savings.
The future is bright for onsite reuse
Water reuse technology is being implemented globally, and regulations are advancing to support these systems. Additionally, multiple national and international organizations are working on guidelines to promote successful technology implementation. The National Blue Ribbon Commission for Onsite Water Systems, for example, is a U.S.-based collaboration of scientists, policymakers, and engineers working on international standards for onsite reuse systems which will help to standardize treatment requirements, support onsite reuse design, and make systems more accessible to more projects.
Another key prong of the water reuse story is the public reception to using recycled water onsite. However, consumer interest in sustainability and “green” living across the U.S. has been growing, and the old “yuck factor” perception of water recycling is slowly dissipating. Multiple studies across the U.S. show that renters are positively influenced by sustainable design, 46% of renters stated that green features influenced their renting decisions in a recent AMLI study.
Technology, regulations, and public acceptance are all slowly coming together to support more widespread onsite reuse on a global scale. Onsite reuse can help projects meet water and energy goals, reduce load on municipal systems, save long-term utility costs, and help us win the global fight for water conservation.