Water Reuse in Minnesota: Greywater

By: Erin Cowles

Introduction

While Minnesota is the “Land of 10,000 Lakes,” it is not immune to the human demand imposed on freshwater sources. In 2013, Minnesota used 200 billion gallons for public supply, 101 billion for industrial processing, 133 billion gallons for irrigation, and 64 billion gallons for other activities, which include air conditioning, construction, water level maintenance, and pollution confinement (Minnesota Department of Natural Resources, 2014). Public water supply is water that is distributed by a supplier for domestic, commercial, industrial, and public users (Minnesota Department of Natural Resources, 2014) and is required to meet national standards under the National Primary Drinking Water Regulations, also known as NPDWRs or primary standards (United States Environmental, 2014a). These standards include maximum contaminant levels for microorganisms, disinfectants, inorganic chemicals, organic chemicals, and more (United States Environmental, 2014a). In municipalities across Minnesota, any water sent to households must be treated to this level.

Treatment plants are typically the largest energy consumers for municipal governments, using 30-40 percent of total energy (United States Environmental, 2014b). On a national level, treating water and wastewater accounts for 3-4 percent of total energy use (United States Environmental, 2014b). In Minneapolis, the drinking water treatment plant uses more energy than any other city owned building and accounts for 50 percent of the electricity and natural gas used in City buildings (B. Slotterback, personal communication, March 30, 2015). As the demand for water grows, more water is extracted, treated, and transported, all of which require energy. Yet not all public supply water is used for human consumption; households use it for lawn irrigation, car washing, toilet flushing, and more, some of which never comes in contact with people. Similarly, municipalities use tap water for water features and to irrigate parks. For instance, the increased demand for water to irrigate lawns in the summer requires a corresponding increase in capacity at water treatment plants (Minnesota Department of Natural Resources Waters Division, 2001). These are a few of the reasons that some states have implemented water reuse techniques.

One such water reuse technique is greywater. Greywater is water from bathtubs, bathroom washbasins, and clothes washers; it does not include wastewater from kitchen sinks, dishwashers, or laundry water from soiled diapers (Water Reuse Interagency Workgroup, 2014b). When treated, greywater could then be used for irrigation, toilet flushing, and other non-potable, non-human uses, which would reduce the demand for water, as greywater systems use the same water twice before the water is sent to the wastewater or environmental system. However, there is a need to balance the potential risks to human and soil health with the benefits of reduced water demand, protection of sensitive ecosystems, and reduced energy demand for treatment and pumping, if greywater is to be implemented.

Water Reuse Options and Use in Minnesota

In Minnesota, water reuse implementation would be determined by state agencies or the legislature. Water and water reuse applications are managed and regulated by multiple state agencies, with each agency holding a separate function around water, summarized in Table 1. Water regulatory bodies in Minnesota span an array of areas including plumbing (Department of Labor and Industry and the Plumbing Board), public health (Minnesota Department of Health), allocation of water resources (Minnesota Department of Natural Resources), water for irrigation (Minnesota Department of Agriculture), water treatment and planning for the Twin Cities metropolitan area (Metropolitan Council), and stormwater and wastewater treatment (Minnesota Pollution Control Agency). These agencies form the Water Reuse Interagency Workgroup (WRIW) in order to develop a consistent message across agencies around water reuse applications. In support of this work, the WRIW is gathering information needed to build an efficient and understandable regulatory and implementation framework that balances the benefits to ecosystems while protecting public health (Water Reuse Interagency Workgroup, 2014a). Water reuse, as considered by the WRIW, is reclaimed water, stormwater, rainwater, or greywater (Water Reuse Interagency Workgroup, 2014b).

Table 1. Minnesota Agencies, Their Functions/Purpose and Water Reuse Interest
Agency Function/Purpose Water Reuse Interest
Minnesota Department of Natural Resources (DNR) Allocates surface and groundwater resources Reusing water to limit pressure on water withdrawals from sensitive ecosystems, but concerned about pathogens entering sensitive ecosystems from water reuse.
Minnesota Pollution Control Agency (MPCA) Oversees wastewater and stormwater systems Interested in improving water quality and stormwater management
Minnesota Department of Labor and Industry (DoLI) Oversees plumbing inside buildings, both public and commercial Changes in plumbing code to allow water reuse could mean further inspections, new plumbing techniques
Plumbing Board Sets plumbing code standards Sets any new water reuse codes that involve plumbing
Minnesota Department of Health (MDH) Protecting wellheads (the source of public drinking waters) and human health Concerned with pathogens and human health implications of water reuse
Minnesota Department of Agriculture (MDA) Monitors drinking water for fertilizer and pesticide contamination, provides technical assistance to farmers Interest in how water reuse can help meet irrigation needs, reduce pressure on water resources
Metropolitan Council (Met Council) Monitors water quality, treats wastewater, creates long-term water supply plan for the seven-county Twin Cities metropolitan area Has created a stormwater management guide

As of 2012, Minnesota reuse projects include five for golf course irrigation, one for building toilet flush water, one for wetland enhancement, one for energy plant cooling water, and 32 for non-food crop agricultural irrigation (United States Environmental, 2012, pg. 5:28).  Treated municipal wastewater is considered reclaimed water (United States Environmental, 2012, pg. 1:4).  In Minnesota, an example of reclaimed water use is the Mankato power plant.  The city provides up to 6.2 million gallons per day of reclaimed water to the Mankato Energy Center (United States Environmental, pg. 5:28). Instead of drawing on additional groundwater sources, the Mankato plant is reusing water that has already been withdrawn, used, and treated.

Stormwater harvesting is the at-grade capturing of water runoff from precipitation events for later use.  Target Field collects stormwater, treats it, and uses it to irrigate the field, reducing city water use by 2 million gallons per year (Metropolitan Council, 2011, Case Studies, p. 6-7).  Another example comes from the City of Saint Anthony Village, which captures stormwater from city streets, treats it, and then uses it for irrigating the St. Anthony City Hall campus and municipal park, saving the city about 4.6 million gallon of water per year (Metropolitan Council, 2011, Case Studies, p. 4-5).

Rainwater harvesting captures precipitation from roofs and porches for later use.  The Schaar’s Bluff Gathering Center in Dakota County utilizes rainwater harvesting for toilet flushing, reducing water use (Dakota County, 2014). The WRIW does not know of any current (2015) greywater projects in Minnesota.

Greywater Use in Minnesota

The state has very few laws and regulations around water reuse technologies, as there has not been demand for these alternative water sources.  However, TheMinnesota Water Sustainability Framework specifically states that, “water reuse policies are needed for Minnesota in anticipation of the time when there will be sufficient demand for reused water” (Swackhamer, et al., 2011, p. 30). While that time has yet to come, the largest city in the state – Minneapolis – calls for a reduction of wastewater treatment impacts, including options for using greywater systems in itsClimate Action Plan (City of Minneapolis, 2013, p. 34).  However, greywater systems are currently not addressed by the Minnesota Plumbing code.  Nonetheless, in Minneapolis, the Building Official can permit an alternative installation that uses greywater, if it follows the instructions set out in the International Plumbing Code or another code where greywater use is allowed (City of Minneapolis, n.d.).

Minnesota Statute 115.59, which expired in 2014, allowed for greywater systems as long as they maintained separation between greywater and blackwater (water from toilets or other sources with high level of fecal contamination), and treated greywater to specific standards (Advanced Treatment Systems Act). This permitted the Equaris system, which took greywater through several filters, reverse osmosis, and ultraviolet light for disinfection, surpassing drinking water quality standards, though at a high cost to the user (National Small Flows Clearinghouse, 2002).  Despite this system being available for sale, there was limited use due to its cost (M. Wespetal and A. Anderson, personal communication, September 9, 2014) and the company with this system appears to be out of business.

At this time, only Minnesota Administrative Rule 7080.2240 covers greywater systems in Minnesota. It incorporates rules on technical requirements, separation from toilet water, and sewage tank size, falling under the Minnesota Pollution Control Agency authority (Gray Water Systems Act). However, despite this rule being in place, greywater use is not yet covered in the Minnesota Plumbing Code. It will not be covered under the current revision but will be up for discussion in the next Plumbing Code revision, which will be in four to six years. Although the Minnesota Plumbing Code does not cover greywater systems, large cities in Minnesota been granted allowances by the State to permit greywater systems, as long as a plumbing code, such as the International Plumbing Code, is used (City of Minneapolis, n.d.).

In cold weather climates, protecting a greywater system from freezing is a challenge that must be considered, especially in Minnesota.  A few examples of greywater reuse in cold climates for residential users include use in a greenhouse and running greywater into a wetland system (“Systems for cold climates including wetlands,” n.d.). There are commercial greywater systems available as well. If greywater were to be allowed, it would probably be used as is typical for states that have permitted greywater use – for on-site irrigation purposes (United States Environmental, n.d.).

National and International Greywater Examples

Arizona has been at the forefront of greywater legislation and practices, creating rules based on surveys of existing systems and setting performance standards, rather than mandating design criteria (Pedersen, et al., 2007).  The laws and codes in Texas, New Mexico, and Montana are all modeled on Arizona’s statutes (Pedersen, et al., 2007). California legalized greywater use in 1992, but it has only been considered partially successful, as it requires specific designs, instead of performance standards (Light House Sustainable Building Centre, 2007, p. 31).  For example, it limits users to certain designs instead of allow any system as long as it treats specific contaminants to a certain level.  Oregon permits greywater use through its Department of Environmental Quality. Depending on the level of treatment, the greywater may be used for subsurface (no treatment) or surface (high treatment) irrigation, as well as toilet flushing (Oregon DEQ, 2012). Montana allows single-family residences to reuse gray water, and legalized all systems installed before the legislation went into effect on October 1, 2007 (Pedersen, et al., 2007).  Washington allows subsurface irrigation for ornamental (non-food) plants with greywater (Light House Sustainable Building Centre, 2007, p. 31).

At the local level, the City of Tucson, Arizona passed an ordinance that requires all new single family and duplex residences to separate discharge of greywater for direct irrigation (Sheikh, 2010, p. 15-16).  Cities in California offer subsidies for greywater kits and permit application fees (Combs, 2014, p. 13).  Nine cities in Texas allow or are planning to allow greywater systems (Combs, 2014, p. 13).  It has been found that greywater installation could save a family of three about 43,000 gallons of water annually in Texas (Combs, 2014, p. 13).  This is a decrease of about 43 percent (Combs, 2014, p. 13), and the amount of water that would be used to irrigate a half-acre parcel of land for three weeks.[1] Yet at a water rate of $2-$4 per 100 cubic feet of water (approximately 748 gallons),[2] this is an annual savings of $115 to $230 for this family of three.

Australia appears to be at the forefront of implementing greywater reuse as the key to residential water conservation.  Not only is irrigation allowed, it may also be diverted for toilet flushing and laundry (Light House Sustainable Building Centre, 2007, p. 35).  While not comprehensive or exhaustive, these examples show that greywater use happens around the U.S. and in Australia, typically in areas that are water limited, either by climate or by water rights.

What are the Benefits and Concerns?

There are multiple benefits to greywater reuse, including addressing supply side demand, conserving energy and protecting ecosystems that are sensitive to water reductions. In its “2012 Guidelines for Water Reuse,” the EPA recommends including greywater as an alternative source in supply side water management (pg. 2:31).  The installation of greywater systems can reduce potable water use, by using a supply of already used water for non-consumption purposes  (United States Environmental, 2012, pg. 2:33). Where water is scarce, greywater reuse can provide a more dependable water supply with local control.  Greywater reuse systems have been operated successfully for many years and have been shown to meet up to 50% of a property’s water needs through irrigation use (United States Environmental, n.d.). As the demand for water grows, more water is extracted, treated, and transported, all of which require energy. Greywater involves less treatment than what is required by public supply systems, as people do not consume greywater (United States Environmental, n.d.). Reusing lower quality water for non-human consumption purposes saves energy and money by reducing treatment requirements (United States Environmental, n.d.). In addition, water reuse can decrease the diversion of water from sensitive ecosystems (Light House Sustainable Building Centre, 2007, p. 31). If too much water is withdrawn from a sensitive ecosystem, the flow rate is negatively impacted, which hurts the biota in and around the stream (United States Environmental, n.d.). A few communities, such as White Bear Lake, in the Twin Cities metropolitan area have surface waters and wetlands that are already affected by current withdrawal rates (Metropolitan Council, 2010, p.11).

At the same time, however, application of greywater can negatively impact surface water if it is applied too close to a waterbody (Light House Sustainable Building Centre, 2007, p. 15). Moreover, use of non-toxic and low-sodium soap and personal care products is required to protect vegetation and the soil, or the greywater would need some initial treatment (United States Environmental, n.d.).  Otherwise, greywater irrigation can result in accumulation of surfactants and antimicrobials in soil (Sharvelle, et al., 2012, p. 4-3).  Greywater affects the pH and electrical conductivity of the soil (Pinto, et al., 2010; Rodda, et al., 2011).

It can also affect capillary action in soils, creating water-repellent soils, which can impact soil productivity (Wiel-Shafran, et al., 2006).  This can have detrimental impacts on the productivity of the soil as the soil becomes more hydrophobic, though it can take several years before these issues arise.[3]  Soil water retention following irrigation is reduced significantly when it is done with greywater (Misra, et al., 2010).  Raw greywater may significantly change soil properties that can impact the movement of water in soil and the transport of contaminants in the topsoil (Travis, et al., 2010).  Irrigating with a mix of potable and greywater can reduce the soil health risks (Pinto, et al., 2010).  Therefore, it may be important to take precautions against sodium and metals using effective treatment methods or a mix of greywater and tap water (Pinto, et al., 2010).

Greywater use also has unique implications for human health, especially potential exposure to pathogenic bacteria and viruses.  This exposure may occur through direct contact with greywater, exposure to areas irrigated by greywater (Cohen, 2009, p. 4), and risks from aerosolized water droplets from greywater toilet flushing (A. Anderson, personal communication). These risks are considerably higher for untreated or partially treated greywater (United States Environmental, 2012, pg. 2:33).  Due to these concerns, the revised 2007 California Plumbing Code includes limits on the direct reuse of untreated greywater for landscape irrigation to drip irrigation, prohibiting spray irrigation (Cohen, 2009, p. 4).  Systematic research on greywater as a public health issue is virtually nonexistent (United States Environmental, 2012, pg. 2:33); the argument of the WRIW has been that more research should be done on this issue before permitting greywater use. There have been no documented cases in the United States of diseases caused by greywater exposure (United States Environmental, 2012, pg. 2:33).

Policy Challenges for Greywater Implementation

There is significant interest in water sustainability in Minnesota and nationally.  Water reuse has the potential to reduce demand on water resources.  There are major regulatory barriers to greywater use in Minnesota regarding inspections, maintenance, logistics, risks, and funding (Water Reuse Interagency Workgroup, 2014a).

Regulations. Institutional barriers, as well as varying agency priorities and public perceptions, can make it difficult to implement water recycling and reuse projects (United States Environmental, n.d.). Current agency structures hinder greywater implementation.[4] For example, the State has statutory authority, while the Plumbing Board makes the code rules for plumbing. The Minnesota Department of Health oversees plumbing from source water to the residence. The Department of Labor and Industry is in charge of plumbing in public and commercial buildings. The Minnesota Pollution Control Agency oversees the removal of sewage. Therefore, any policy around greywater has to manage falling under the purview of many agencies while also being clear about which agency manages which component. Water policy in Minnesota is very complex, as there are already multiple agencies involved in managing the flow of water from source, to treatment, to a tap, from the tap to wastewater without adding water reuse to the mix. Agencies are unsure what action – if any – to take on greywater research, as there is currently a lack of codes.

There are no national regulations or guidance on greywater, although a global public health and environmental organization, NSF International, has published the first national standard for commercial and residential onsite water reuse treatment systems (United States Environmental, n.d.).  At the state level, there is a lack of agreement as to whether greywater systems should be guided or fall under standards – a difference in strictness and penalization.  Some agency definitions may need to be changed to include greywater, or else the agencies would not have legal right to create standards and regulations.  Finally, stringent regulations could be a barrier to implementing greywater reuse and other forms of reuse.

Inspections. If greywater systems were implemented, who would perform inspections and verify their performance over time? In Minnesota, this is made more challenging as different agencies have authority at different parts of the plumbing system. Also, there is the possibility that cross-connections with potable water supplies could result in a contamination, especially in instances where greywater and drinking water come together to meet toilet flushing or irrigation demand.  If every individual house were to have a residential greywater system, it could result in a nightmare for overseeing agencies, assuming inspections were required.

Logistics. Logistics includes storing greywater for later use as well as meeting demand for greywater when it is needed. For example, demand for greywater for irrigation is higher in the summer than in the winter. For example, in the outer suburb of Andover, Minnesota, the city sometimes pumps six times as much groundwater during hot, dry summer days as it does during the winter (Dunbar, 2010).  Nationally, nearly one-third of all residential water use goes toward landscape irrigation (United States Environmental, 2013).  In Minneapolis, the average residential customer uses around 60-70 gallons per day (City of Minneapolis, 2015); based on the national average, approximately 8,400 gallons per residential customer are used per year on landscaping needs in Minneapolis.

Even if greywater was available for use, there might not be a way to use it at that time.  For example, if greywater use is limited to irrigation, this means any greywater produced from October to March would either be wasted or need to be stored over winter for use in spring. An inventory of household water use shows that outdoor water use during the summer – for vehicle washing, irrigation, etc. – typically exceeds greywater creation. On an average day, a household uses 100 gallons of water for outdoor uses versus 37.5 gallons from faucets, clothes washers, and showers (Mayer, et al., 1999), what the state of Minnesota considers greywater.  Saving greywater collected during the winter would amount to approximately six- to seven-thousand gallons per residential household.  At the same time, water storage poses its own challenges due to space and weight constraints. The amount of greywater stored during half a year in Minnesota would take up about 900 cubic feet, the size of a 10’ x 10’ bedroom with nine foot ceiling, and weigh over 28 tons, the size of over four male African elephants.[5]  Purchasing underground tanks to hold this amount of water is a cost that residents may not be willing to undertake.

If it is not economically viable to store greywater during winter months, each household could still save about 37.5 gallons of water per day (Mayer, et al., 1999) during summer and fall by using greywater for some irrigation needs instead of only using tap water. This could be helpful, especially in Minneapolis. About 55-60 percent of annual residential (buildings with four or fewer households) use in Minneapolis occurs from May to October, approximately 450 million to 800 million more gallons than the months of November to April.[6]  Some of this increase can be attributed to landscape irrigation. The state of Minnesota needs to consider if a savings of about 37.5 gallons per household per day during the summer would be worth the cost of implementation. At this time there is no comprehensive study that looks at the economic viability of greywater use in Minnesota.

Risks. There is a lack of consensus around health risks related to reuse applications.  Minnesota has not decided what water quality standards – if any – would need to be met to protect human and environmental health.  The Minnesota Department of Health is beginning to explore the pathogen and health risks associated with all water reuse sources.  Currently, state regulations or guidance for nonpotable reuse are not uniform across the country and no state has based their water reuse regulations or guidelines on rigorous risk assessment methodology (Minnesota Pollution Control Agency, 2015).

Cost.  Beyond logistical costs of storage, costs also include the extent and method of treatment required, infrastructure and equipment such as a second set of pipes and tank storage, monitoring of water quality parameters, and regulatory oversight.  Systems can be simple and cost only a few hundred dollars (Combs, 2014), while more complex systems like Equaris can cost upwards of $20,000 (National Small Flows Clearinghouse, 2002, p. 6).  At the same time, state agencies have little funding to begin exploring the costs and needed regulations.  It is important to balance these costs with the benefits of reduced water demand, protection of sensitive ecosystems, and reduced energy demand for treatment and pumping.

Recommendations

To deal with these policy challenges, the State of Minnesota should consider doing more research on greywater and other reuse options to better understand which are the best reuse strategies for the state. Before doing so, the legislature needs to help determine which agency has primary regulatory authority and which agencies will be collaborating agencies for regulating greywater. The agencies are required to use their funds for their delegated authority, so giving the agencies a better idea of their responsibilities under water reuse, through administrative rules, will allow them to move forward. Next, using this new understanding of what agencies control what aspects, the WRIW should begin to focus on the regulations of inspections and the greywater systems that may work best in Minnesota, including what may be most cost effective for residential users.

In addition, the WRIW should continue to research the risks of greywater use, and what treatment and collection methods might decrease these risks. If the agencies are unable to fund the research done by the WRIW, one potential source of funding is the Clean Water Legacy Fund. Controlled by the Clean Water Council, this fund distributed approximately $194 million in fiscal years 2014-2015, including money to state agencies (Clean Water Fund, 2013). These steps would help agencies better understand their authority and allow them to begin exploring water reuse technologies, including greywater.

Conclusion

Greywater is the last water reuse technique, of the four defined by the WRIW, to be implemented in Minnesota. This is mostly due to the fact that Minnesota has enough water to meet demand, although there are demand pressures being felt in a few areas of the state.[7]  This may change though, as water demand continues to increase faster than population growth, a trend that has been happening for the past 25 years in Minnesota (Environmental Quality Board, 2012, p. 2). In the Twin Cities metropolitan area, residential demand alone is expected to grow by 75 million gallons per day (Metropolitan Council, 2010, p. 3-14), an increase from 230 million gallons used currently (Metropolitan Council, 2010, p. 3-1, 3-3). Greywater has been shown to reduce water supply demands, along with protecting sensitive ecosystems and reducing energy demand.

At some point, though there have been no specific studies done on the year it may become necessary, Minnesota could feel the need to implement greywater use, as has been done in states with drier climates to match demand pressures. It is important that the state of Minnesota begin researching the water quality standards needed for greywater, the applications and designs that are most effective for Minnesota’s climate, and carefully consider the benefits and costs before dismissing greywater reuse at present.  Health studies, regulatory research, and code considerations take time.  By addressing these now, the State of Minnesota can be prepared for a time when there will be sufficient demand for greywater reuse.

 

 References

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[1] Assuming that the household is watering 1 in of water per week over the entire half acre.

[2] The water rate in Fort Worth, Texas is $1.97 per 100 cubic feet (http://fortworthtexas.gov/water/info/default.aspx?id=117022), $1.99 per 100 cubic feet in Austin, Texas (https://www.austintexas.gov/sites/default/files/files/Water/Rates/Approv...), and about $3.70 per 100 cubic feet in Houston (http://edocs.publicworks.houstontx.gov/documents/divisions/resource/ucs/...). The rate of water per 100 cubic feet in Minneapolis, MN is $3.37 (http://www.ci.minneapolis.mn.us/utilitybilling/faq/utility-billing_about...) while the price per 100 cubic feet is $2.52 in winter and $2.62 in summer for St. Paul customers (http://mn-stpaul.civicplus.com/DocumentCenter/Home/View/3493). These rates do not include meter and sewer charges, which are sometimes based on water consumption rates. The price fluctuates by utility and by the location.

[3] Sharvelle, et al. found that five years of greywater use did not raise concern for soil or plant health.

[4] Knowledge comes from the author’s participation on the Water Reuse Interagency Workgroup and conversations with Cathy Tran (Department of Labor and Industry).

[5] Calculations by author. 37.5 gallons of greywater created each day from October to March. Creation of 37.5 gallons of greywater per day* approx. 180 days = 6,750 gallons of greywater produced that need to be stored. There are 748 gallons per 100 cubic feet. So 6,750 gallons/748 gallons per 100 cubic feet is approximately 900 cubic feet. Took the weight of 1 gallon of water, which is about 8.34 lbs. Therefore, 6750 gallons x 8.34 lbs / 12,000 lbs (the average weight of a male African elephant) = over 4 male African elephants.

[6] Water data from 2006-2012, requested and received from the Minneapolis Sustainability Office.

[7] For example, White Bear Lake, northeast of St. Paul Minnesota: http://www.startribune.com/local/east/284350031.html