On-site Alternative Water Reuse

What is On-site Alternative Water Reuse?

On-site alternative water reuse intentionally captures, treats, and utilizes stormwater, graywater, and wastewater for reuse at the building site. Stormwater includes precipitation such as rainfall and snowmelt. Graywater (also spelled gray water, greywater and grey water) refers to untreated water from bathroom sinks, laundry, and bathing and does not include water contaminated with toilet waste, food and grease content from kitchen sinks, or dishwasher soap residue.[1] Graywater is of lesser quality than potable (drinking) water but of higher quality than blackwater, which in New Jersey refers to wastewater from water closets, toilets, and urinals.[2] Potential sources of onsite alternative water include rainwater, treated graywater and blackwater, condensate from air conditioners, reject water from water treatment systems, and cooling equipment blowdown.[3] Figure 1 shows examples of end-uses for on-site alternative water reuse such as irrigation, cooling tower make-up water, and toilet and urinal flushing.

Figure 1 – Examples of On-site Alternative Water Reuse. (Source: US EPA WaterSense at Work)

How to Implement Onsite Alternative Water Reuse

Implementing on-site alternative water reuse starts with water conservation and includes identifying and evaluating opportunities to substitute or supplement potable water use with on-site alternative water sources based on the water quality and treatment requirements of the intended end-uses, and the feasibility of capturing and delivering alternative water sources to those end-uses (see Indoor Water Conservation).

Harvest and filter rainwater from rooftops to supplement or replace landscape irrigation and toilet and urinal flushing (see Rain Barrels and Cisterns, Vegetated Roofs, and Emergency Water Supply and Storage).[4] Rainwater that flows over parking lots and impervious hardscapes and filtered by rain gardens or captured by retention ponds also provides an alternative water source for landscape irrigation (see Rain Gardens, Water Efficient Landscaping).

Capture graywater from fixtures and appliances by designating separate drain lines, storage units, and pumps to deliver graywater to desired locations. Graywater used for subsurface irrigation of trees, shrubs, and flower gardens requires filtering to remove suspended solids. Indoor uses for graywater such as toilet and urinal flushing, or above-ground irrigation for turf grass or edible gardens often require additional treatment through natural, mechanical or chemical applications.[5] Treatment systems include engineered systems, tailored to specific projects, and packaged systems designed to fit a wide range of project applications.[6]

Reuse wastewater from building applications and processes for use in another onsite applications. For example, use condensate from air conditioners for cooling tower make-up water or subsurface irrigation. Use water rejected from water treatment systems for a range of end-uses that do not require potable water such as toilet and urinal flushing, cooling tower make-up water, above-ground irrigation, and decorative water features.[7]

Blackwater treatment systems require a higher level of treatment to bring recycled water to acceptable standards for reuse. Constructed wetlands use a combination of plants, snails, clams, algae, and fish to filter and break down compounds in blackwater. Commercial treatment systems may include sedimentation, membrane filtration or UV sterilization. Composting toilets provide another way to reduce potable water use and reduce the need for wastewater treatment.

Hire certified professionals familiar with the design, construction, and maintenance of onsite alternative water reuse systems. Review local ordinances, permitting requirements, and plumbing codes.

The International Association of Plumbing and Mechanical Officials Green Plumbing & Mechanical Code Supplement provides guidance on implementing onsite alternative water reuse for non-potable end-uses.

The NSF International/American National Standards Institute (NSF/ANSI) 350, Onsite Residential and Commercial Reuse Treatment Systems establishes design, construction and performance requirements for onsite alternative reuse systems.

Example

The Solaire, New York City

The Solaire, a LEED Gold certified residential high-rise building in Battery Park completed in 2003 offers examples of on-site alternative water reuse and wastewater treatment technologies applicable to new commercial buildings. Indoor water conservation measures include low-flow fixtures, toilets, and appliances that reduce potable water use by 43%. The building’s onsite wastewater treatment plant utilizes digestion, membrane filtration, and ultraviolet disinfection to processes 30,000 gallons of blackwater each day and reuses it as cooling water for two on-site cooling towers and to flush toilets in both the Solaire and an adjacent building, the Verdesian. The Solaire’s vegetated roof helps manage stormwater and diverts excess stormwater runoff to a 10,000-gallon basement water storage tank that stores the water for later use by the vegetated roofs drip irrigation system.

Benefits

On-site alternative water reuse reduces potable water use and the reliance on surface water, groundwater, and reclaimed water purchased from a third-party.[8] Harvesting rainwater can reduce stormwater runoff, flooding, and pollution. Graywater and blackwater reuse reduces the strain on municipal water and wastewater treatment plants. Compared to potable water, recycled water used for irrigation often contains higher levels of nutrients, such as nitrogen, that lessens the need for synthetic fertilizers. On-site alternative water reuse reduces the energy required to transport water or pump water from deep underground sources. Using recycled water for applications that do not require water treated to potable or drinkable water quality standards saves energy and money by reducing treatment requirements.

Costs

The rising cost over the last decade of water and wastewater services can make minor investments in water conservation strategies and onsite alternative water use technologies cost-effective based on the savings alone from reduced water bills.[9] Factoring in savings from reduced energy bills further reduces payback periods. As on-site alternative water technologies evolve, and costs decline, and water shortages and water quality issues become more common, the resiliency benefits of a local and reliable water resource on reduced business closures, health and safety hazards, and inconvenience from schedule disruptions, can offset the incremental costs. [10]

Resiliency

Using on-site alternative water resources enhances resiliency by utilizing safe, reliable, redundant and locally controlled water supplies, by reducing impacts from droughts and other instances of water scarcity, and by protecting sensitive, natural water bodies. Reducing potable water use reduces the reliance and stress on the entire municipal water infrastructure including groundwater pumping, and water and wastewater treatment and distribution, reducing the likelihood of system overload and failure (see Emergency Water Supply and Storage).[11] Many water pumps run on electricity, and without a source of backup power, fail to operate during power outages highlighting the importance of on-site alternative water sources and treatment options that cover all or part of onsite water use and wastewater treatment needs (see Energy Storage and Backup Power Generation). Compostable toilets also increase resiliency by continuing to operate during water shortages and by preventing sewage backups.

[1] Alliance for Water Efficiency. 2018. Graywater Introduction. http://www.allianceforwaterefficiency.org/graywater-introduction.aspx (accessed Nov 15, 2018).

[2] NJ DEP. Division of Water Quality. Standards for Individual Subsurface Sewage Disposal Systems. www.state.nj.us/dep/dwq/pdf/njac79a.pdf (accessed October 22, 2018).

[3] US EPA. 2012. WaterSense at Work: Best Management Practices for Commercial and Institutional Facilities. https://www.epa.gov/sites/production/files/2017-02/documents/watersense-at-work_final_508c3.pdf (accessed Nov 14, 2018).

[4] US EPA. 2012. WaterSense at Work: Best Management Practices for Commercial and Institutional Facilities. https://www.epa.gov/sites/production/files/2017-02/documents/watersense-at-work_final_508c3.pdf (accessed Nov 14, 2018).

[5] US EPA. 2012. WaterSense at Work: Best Management Practices for Commercial and Institutional Facilities. https://www.epa.gov/sites/production/files/2017-02/documents/watersense-at-work_final_508c3.pdf (accessed Nov 14, 2018).

[6] Alliance for Water Efficiency. 2018. Graywater Introduction. http://www.allianceforwaterefficiency.org/graywater-introduction.aspx (accessed Nov 15, 2018).

[7] US EPA. 2012. WaterSense at Work: Best Management Practices for Commercial and Institutional Facilities. https://www.epa.gov/sites/production/files/2017-02/documents/watersense-at-work_final_508c3.pdf (accessed Nov 14, 2018).

[8] US EPA. 2012. WaterSense at Work: Best Management Practices for Commercial and Institutional Facilities. https://www.epa.gov/sites/production/files/2017-02/documents/watersense-at-work_final_508c3.pdf (accessed Nov 14, 2018).

[9] Joseph Bourg. 2016. Water Conservation. Whole Building Design Guide – A Program of the National Institute of Building Science. https://www.wbdg.org/resources/water-conservation (accessed Oct 26, 2018).

[10] DOE. “Smart Grid Investments Improve Grid Reliability, Resilience, and Storm Responses.” https://www.smartgrid.gov/files/B2-Master-File-with-edits_120114.pdf (accessed May 1, 2018).

[11] Joseph Bourg. 2016. Water Conservation. Whole Building Design Guide – A Program of the National Institute of Building Science. https://www.wbdg.org/resources/water-conservation (accessed Oct 26, 2018).