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Greywater Reuse: A
Valuable Water Resource
Katie Keefe
April 2013
The Greywater Initiative
Saving Water Drop by Drop
30 Westgate Parkway, No. 121
Asheville, NC 28804
Greywater Recycling
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ABSTRACT
In response to the problems of water supply shortages, changing hydrological conditions
and population growth, greywater recycling has emerged as an adaptive strategy to meet the
growing domestic water demands of the Earth’s inhabitants. Greywater, defined as wastewater
collected from sinks, bathtubs, and clothes washers, does not include wastewater from urinals or
toilets, presenting an additional, useable source of freshwater. Communities facing the most
imminent threats to water stability include water scarce regions, peri-urban, and rural
communities in the developing world. Recycling greywater at household scales for agricultural
and other domestic purposes can increase economic productivity, foster sustainable food
production, and increase water resource resiliency in these communities. Numerous small-scale
greywater recycling projects implemented in these regions show that greywater can be used in a
safe and effective manner to meet domestic and agricultural water demands. Though grewyater
recycling has the potential to stretch water resources, there are legitimate concerns regarding the
safety of its use. By understanding its impacts and mitigating associated environmental and
public health risks in a framework that matches the needs of the community, greywater recycling
will be instrumental in addressing the water challenges of the 21st century.
BACKGROUND
A finite amount of fresh water continually recycled within the Earth’s hydrological cycle,
is available for human consumption. While there may appear to be a large amount of water on
the planet, only 2.5% is freshwater and only 1.4% of that total can be accessed and used for
agricultural, industrial, and domestic purposes (Kenny et al. 2005). Water plays a critical role in
both human and ecosystem health and is essential for sustainable food, energy and economic
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development (Hanjra et. al 2012).
The quantity and quality of freshwater supplies vary
depending on the natural topography, climate, ecosystem properties and human based influences
of the region (Jurkowski 2010).
History demonstrates that access to sanitation services and safe
freshwater influence human living conditions and environmental health (Watkins 2006). Since
water resources are necessary for the production of crops, livestock, goods, and energy, the
demand for water is rising with growing populations and their economies. According to two
recent reports on the current state of global water resources, almost all nations face challenges
regarding the availability and quality of freshwater resources (Bates 2008; Watkins 2006).
Urbanization, industrialization, and agricultural production can alter the water quality
through
pollution
mechanisms
and
decrease
availability
through
overconsumption.
Overconsumption of water by all sectors can permanently alter aquatic ecosystems and land, as
observed with aquifer salinization (Cardona et. al. 2004) and land subsidence (Flowers 2004),
respectively. If not addressed by comprehensive management strategies, the increasing demand
for water coupled with inefficient consumption by agriculture and industry will potentially lead
to an increase in water shortages and further water scarcity problems in in arid and semi-arid
regions of the world (Molden et al. 2007).
Water scarcity, as defined by the United Nations (2007) is, “the point at which the
aggregate impact of all users impinges on the supply or quality of water under prevailing
institutional arrangements to the extent that the demand by all sectors, including the
environment, cannot be satisfied fully (p.4)”. The UN estimates that around 1.2 billion people –
or almost one-fifth of the world's population – live in areas where freshwater resources are scarce
and another 1.6 billion people – or almost one quarter of the world's population – face economic
water shortages from a lack of system infrastructure (UN-Water FAO 2007). These salient water
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supply issues present an imminent threat to food security and human health in many parts of the
developing world (Menegaki, Hanley, and Tsagarakis 2006). Joint efforts made over the past
decade by national governments, international organizations and non-profit organizations have
increased the percentage of people worldwide that have direct access to improved sources of
drinking water; however, the number of peri-urban dwellers lacking access to drinking water and
sanitation services continues to rise as services cannot keep up with rapid urbanization of
population centers (Connor and Loucks 2012).
Centralized systems of water governance are common in the developed world where
infrastructure for water distribution and sanitation services are in place. In most rural and periurban regions of the developing world the lack of water supply infrastructure poses significant
risks to food security, human health and economic viability (Maimon, Tal, Friedler and Gross
2010). Decentralized governance, however, also allows communities to more quickly respond to
resource challenges at the local-scale (da Costa Silva 2011).
Greywater recycling offers
decentralized water governance systems a dynamic response to water shortages with benefits that
include reduced water extraction, energy savings and increased food security (Hanraj et al.
2012). As communities experience shortages in water supply, they often turn to wastewater as a
water source for crop irrigation (Menagaki et al. 2007). As discussed below, the potential for
greywater recycling to increase agricultural yields, lessen the costs of wastewater treatment, and
provide a drought-resistant source of water must be balanced by any negative impacts its use
may have on soil health (Al-Hamaiedeh and Bino 2010), groundwater, and surface water quality
and human health (Maimon et al. 2010; Toze 2006; Revitt et al. 2011).
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GREYWATER DEFINED
Wastewater generated from bathing and washing activities is known as Greywater. The
World Health Organization defines greywater as untreated household wastewater that has not
come into contact with wastewater from toilets and urinals (WHO 2006). Within the United
States, wastewater from kitchen sinks is excluded and in some cases, prohibited by municipal
regulation, from grewyater collection systems. Greywater comprises a large majority of a typical
household’s overall wastewater stream. In the U.S., greywater constitutes up to 60% of a singlefamily’s wastewater discharge (Donner, Erickson & Revitt 2011). In other regions of the world,
this percentage varies depending on how water is used within the household (Al- Jayyoud 2010)
but, typically comprises 50-65% of wastewater from households in developing countries
(Maimon et al. 2010). Recycling greywater for domestic uses and household irrigation can
reduce domestic water consumption by up to 50% (Maimon et al. 2010). This reduction in
consumption could help ameliorate the stress placed on already strained water resources, as well
as lighten the work load of those tasked with obtaining water for daily household use.
Greywater, though mostly water, does contain elements typically associated with
municipal wastewater streams. The quality of greywater depends largely on the water sources
feeding into the system, for instance whether the source is strictly a utility sink, or a combination
of bathroom sink, wash basin and kitchen sink.
Though recommended for water quality
concerns, excluding kitchen water from household or community systems within the developing
world is often untenable due to existing water supply systems (Fiedler 2005). Water from food
preparation activities can increase the micro-nutrient load and potential for microbiological
contamination of greywater (Fiedler et al. 2006). The non-water portion of greywater (GW) can
contain suspended or dissolved solids, metals, mineral salts, xenobiotics, oils, surfactants,
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microorganisms, and biological matter (Roesner et al. 2006; Hanjra and Blackwell 2011).
Common contaminants that are measured in municipal wastewater to help determine necessary
treatment methods can also be measured in GW; these contaminants include chemical oxygen
demand, biological oxygen demand, turbidity, total phosphates, ammonia levels, and total
coliform counts (Maimon et al. 2010). Soaps and detergents used within the household can also
contribute boron, phosphates, mineral salts, and surfactants to the greywater stream.
As
observed by Al-Jayyousi (2003), the large variation in composition can make effective treatment
of greywater difficult (p 184). Where possible, measuring the levels of these contaminants can
assist with assessing exposure risks then determining appropriate treatment methods (Maimon et
al. 2010).
Despite the presence of potentially harmful contaminants, greywater is increasingly being
investigated as a viable water resource alternative (Revitt et al 2010). For instance, water
scarcity and increasing costs of water are main drivers of greywater recycling for crop irrigation
in many areas of the developing world (Scheierling, Bartone, Mara, and Dreschel 2010).
Research focused on assessment and risk mitigation has corresponded with this growing demand
for greywater recycling.
Through characterization, appropriate treatment methods can be
selected for the hazards present and that best suits the end-use of the greywater stream (Maimon
et al. 2010, Revitt 2011, Toze 2006).
Understanding the potential risks associated with
greywater is an important factor in determining the type of treatment system best suited for the
grewyater application and, thus, reducing potential risks to human health and the environment.
Potential Risks to Environmental and Soil Health
Contaminants in greywater may have negative impacts on soil ecology (Al-Hamaeideh
and Bino 2010). It is possible that elevated levels of surfactants, borons, and metal salts may
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alter soil fecundity and may be taken up by plants (Maimon et al. 2010 and Allen et al. 2010).
Increased soil salinity from greywater irrigation can negatively impact the soil’s capacity to hold
water and support growth. Boron salts, a contaminant from soaps and detergents, can be of
particular concern because of their toxicity to plants (Al-Hamaiedeh and Bino 2010). Several
studies have looked at GW impacts on soil salinity levels and nitrogen fixation. One study in
Israel found that soil salinity was elevated in fields irrigated with greywater as compared to those
irrigated with freshwater and that boron was a primary component of the salinity content;
however, this study also revealed that soil degradation could be mitigated by planting salt
tolerant crops such as olive trees (Al-Hamaiedeh and Bino 2010).
It is possible that nutrients found in greywater lead to higher crop yields and can reduce
the need for fertilizer inputs, especially in over-produced land (Hussain, Raschid, Hanjra,
Marikar, and Van der Hoek 2002). While beneficial nutrients present an opportunity to increase
soil fecundity, many metals and minerals found in soaps, detergents and other household
products present a risk to both soil health and potential risk pathways for humans ingesting those
crops. Although elevated levels of minerals and metals have been detected in plants grown in
soil irrigated with greywater (Hanjra, Blackwell, Carr, Zhang, and Jackson 2012), their
concentrations are very low (Al-Hamaiedeh and Bino 2010). Recent research indicates that
occasional flushing of irrigated soils with freshwater could mitigate any long-term detrimental
effects caused by increased salinity, mineral content and increased nutrient load (Al-Hamaiedeh
and Bino 2010).
Oils and surfactants are another common component of greywater that can prove
detrimental to soil and plant health. These materials can cause plants to turn hydrophobic,
thereby limiting growth and fruit yield (Allen et al 2010). Additionally, oils and particulates in
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greywater can alter a soil’s permeability (Bino et al. 2010) and may negatively impact shallow
groundwater sources through soil transfer mechanisms (Jalali and Merrikphour 2008).
Identifying the sources of metals, minerals and salts in greywater could facilitate elimination of
these contaminants. Providing households with information on product substitutions for soaps,
personal care products and detergents is likely to be the most effective hazard control strategy in
developing countries where secondary or complex grewyater treatment systems are not feasible.
Potential Human Health Risks
Microbiological, chemical and physical contaminants in greywater can pose risks to
human health (Toze 2006).
Microbiological content may include pathogenic organisms
including viruses, fecal coliforms, protozoans and helminthes (Maimon et al. 2010). Escherichia
coli are a pathogenic fecal coliform whose presence in water indicates contamination with fecal
matter (Maimon 2010). Analyzing wastewater for coliform bacteria is often used to indicate the
likelihood that pathogenic micro-organisms are present in the wastewater stream (Maimon
2010). Recent research suggests that using total coliform counts as an indication of fecal
contamination may over-estimate the actual level of contamination and wastewater fecal load
(Roesner et al. 2006). Whether screened for coliforms and/or E. coli, protection against direct
contact or accidental ingestion of greywater is warranted. Where high levels of total coliforms
are present, direct handling of raw greywater should be minimized and subsurface irrigation of
crops should be practiced.
Exposure to hazardous components can occur through ingestion or aspiration of raw
greywater, or by ingesting certain plants, vegetables and herbs grown in soil irrigated with raw
greywater. One study of greywater impacts to soil in Israel (Al-Hamaeideh and Borin 2010)
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observed elevated counts of total coliforms in two types of plants irrigated with basic, filtered
greywater (p. 119). This elevated bacterial count may be attributable to the types of crops grown
(i.e., lettuces) or to the lack of chemical disinfection as is often found in small-scale, inexpensive
GW systems.
Mitigating exposure to contaminants can be achieved through the use of protective
equipment when direct handling of the water is necessary or through subsurface irrigation
methods that limit the potential for inhalation or ingestion of the water (Maimon 2010).
An
effective method of controlling the level of microbiological contamination is by maintaining
separation between greywater and black water sources (Maimon et al 2010, Revitt et al. 2011).
Using greywater within 48-hours of collection has also been shown to be effective at controlling
bacterial growth, thus lowering risk of health effects (Al-Jayyousi 2003).
Based on perceptions of risk, some states in the U.S. do not allow households to irrigate
lawns or gardens with greywater (Roesner et al. 2006), while other states allow irrigation but
with clear guidelines governing the parameters of GW collection and treatment. This aversion to
risk may be more appropriate in the U.S. where potable water for crop production is readily
accessible even in water scarce areas. In water scarce and economically challenged regions of
the developing world, prohibiting greywater recycling may in essence deny these communities of
water necessary for crop production and food security. When developing water management
strategies for peri-urban, rural and water scarce communities, the potential health and
environmental risks from greywater use must be balanced against the community’s water needs
and existing water conditions in determining feasible greywater treatment methods.
There are
simple, cost effective GW systems that can limit potential risks when matched appropriately to
the end-use. Treatment technologies, ranging from simple systems used at household scales to
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very complex systems used in large-scale, multi-source reuse schemes, can be employed to
mitigate human health risks to acceptable levels given the context in which the greywater is used.
GREYWATER TREATMENT SYSTEMS
Greywater systems range from simple diversion types to ones that employ complex,
tertiary treatment and disinfection. The former system diverts wastewater directly to its end use,
such as in a drain pipe from a sink that empties directly onto a garden or lawn.
Some
diversionary systems provide basic filtration prior to application to remove suspended solids
(Allen et al. 2010). More complex treatment systems are available and increase in cost with a
corresponding increase in the level of treatment (Allen et al. 2010).
Complex greywater
treatment systems employ filtration, sedimentation, biological, and disinfection treatments prior
to distribution to the end use. In all cases, using greywater within 48-hours of collection helps to
prevent anaerobic decomposition and growth of pathogenic microorganisms (Roesner et al
2006). Conversely, storage for at least 24 hours has been shown to improve the COD, BOD and
TSS content of collected greywater (Dixon et al. 1996).
Diversionary Systems
The most simple greywater system is one in which used water is diverted directly to its
end use without collection or treatment. These systems include designs where greywater from
sinks, wash basins, and/or clothes washers is directly diverted to exterior gardens, trees or
landscapes with minimal to no treatment. Simple diversionary systems are also used to fill
toilets and urinals with water from co-located sinks.
Very simple methods observed in
developing country households entailed collection of wash water into a bucket that is then
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applied directly to soil or reused for other washing activities (Allen et al. 2010). Diversionary
systems do not collect or treat greywater, though some may use simple filtration to remove lint,
hairs and other large particles. It appears from the literature review, that these types of systems
are generally found within households and communities in developing nations that lack
centralized water and sanitation systems. In one Lebanese town, this type of diversionary system
was installed in 70 homes to provide irrigation water to fruit trees and seedlings. The Greywater
system design included natural sedimentation of particulates before pumping of greywater to a
drip irrigation system for fruit trees and seedlings (El-Hajj 2010).
Filtration and Chemical Treatment Systems
Before grewyater can be stored for any length of time, it must be filtered and treated to
some degree to limit the potential for anaerobic activity and bacterial growth. These GW
systems include a collection tank or basin that allows for accumulation as GW is produced.
Primarily, the GW is filtered through physical barriers before collection into a reservoir where it
is treated with a simple disinfectant such as chlorine (bleach).
Treatment with chlorine,
however, can cause the formation of the toxic byproduct, trihalomethanes.
Transport of
trihalomethanes in irrigated soil and uptake into plants has not been extensively studied making
it difficult to assess risk associated with ingestion of irrigated, edible crops. More complex
treatment protocols use ozone or ultraviolet light as a disinfectant during the final treatment
phase. These systems are rarely seen in household-scale greywater schemes in developing
countries (Allen et al. 2010). Both chemical and physical disinfection processes are more
effective when either the initial concentration of biological material and microorganisms in the
raw greywater are low or the previous treatment steps were successful at lowering their levels
(Al-Jayyousi 2003). In household GW systems, this level of treatment in conjunction with quick
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turnover of accumulated greywater can lower bacterial counts thus, lowering human health risks
from direct contact with the water.
Biological Treatment Systems
Treatment protocols that involve biological treatment for removal of biodegradable
material are primarily used in large, community-wide or multi-family distribution networks (AlJayyousi 2003).
Municipal wastewater treatment plants often use a combination of
sedimentation, biological treatment, and disinfection to remove contaminants to safe levels
before discharging to surface waters. Biological treatment systems utilize some form of aerobic
biological treatment to further remove organic contaminants from collected greywater (Allen et
al. 2010). These systems generally mimic municipal treatment plants but on smaller scales and
are expensive to install, operate, and maintain. These types of systems are not generally feasible
in household or small-scale applications in rural and peri-urban areas. Some countries have
successfully used these systems to treat GW from multi-story buildings for urinal and toilet
flushing within the building (Domenech and Sauri 2010). Yet, other countries successfully
treated wastewater using biological systems that incorporated constructed wetlands (Sklarz
2009).
When used to complement centralized sanitation services, on-site tertiary treatment can
produce greywater that is safe for re-use in multi-family dwellings and larger scale reuse
schemes (Fiedler 2005). In these applications, tertiary treatment of greywater for reuse can
decrease the amount of wastewater discharged to surface waters and also decrease demand for
freshwater. Since these treatment methods are more substantial and technical, the costs of
installing, operating and maintaining them can be high (Domenech and Sauri 2010).
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GREYWATER GOVERNANCE AND USE
Many developing countries do not have guidelines or regulations in place regarding the
collection and use of greywater (Al-Jayyousi 2003; Allen et al. 2010). Yet the prevalence of
greywater recycling for crop irrigation and use in domestic tasks is high in rural, peri-urban
(slums) centers and arid regions. The use of greywater and wastewater is often not monitored or
regulated because these communities lie beyond the jurisdiction of local municipalities (Bos
2006). Since water scarce communities may already be using simple, diversionary systems for
GW irrigation (Raude et al., 2009), it is imperative that health education, risk assessment and
risk management campaigns be implemented in these communities to address public health risks.
The World Health Organization has developed basic guidelines to aid in the safe use of
recycled greywater (WHO 2006). The WHO guidelines recommend assessing potential risks
from GW irrigation based on the type of use within the context of the human health and socioeconomic conditions of the community in which it is used (Mara and Kramer 2008). These
guidelines promote a “systems approach to cumulative risk management” that lowers health risks
from greywater use; for instance, using prophylactic treatment and vaccination protocols to
lower the overall prevalence of water-borne and food-borne disease vectors to limit the risks
associated with consuming produce irrigated with greywater (Bos 2006). Assessing crop type,
timing of irrigation, food preparation methods, food sanitation and level of hygiene education
would provide insight into potential, cost-effective measures to lower overall health risks (Bos
2006).
As suggested previously, providing information to communities on product alternatives
could also limit the types and concentrations of physical and chemical contaminants in
greywater. The WHO recommends comprehensive, on-going monitoring to ensure public health
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is protected where greywater is used (WHO 2006). More long-term, epidemiological studies
could illuminate the true nature of greywater risks while providing manufacturers of GW
systems with much needed data for system design (Roesner et al. 2006). Since GW system costs
increase with each level of treatment, matching the intended use with the minimal treatment
necessary to reduce risk could promote more equitable governance structures. As public policy
develops, risks can be managed through public education campaigns and cross-sectorial cost
sharing to incentivize installation and use of greywater treatment systems for irrigation of crops
intended for market sale.
Worldwide Use
Greywater is already used in many rural and peri-urban centers of the developing world.
The World Health Organization estimates that up to 10% of the world’s population consumes
food grown in soil irrigated with wastewater (WHO 2006). In fact, greywater reuse is an
accepted practice in many arid and semiarid regions of the world, comprising 10-40% of total
water use in those regions (Jimenez and Asano 2008). Public perception of greywater and risks
will continue to be a limiting factor in acceptance and use of this water resource in areas with
centralized water systems (Domenech and Sauri 2010). Development of international standards
for greywater treatment and application could significantly improve public perception of risks;
though implementation, adherence to, and oversight of standards could prove to be immensely
challenging.
In the Lebanese town of Tanourra, simple diversionary GW systems installed within 70
households were used to irrigate fruit trees and seedlings grown in gardens (El-Hajj 2010).
There was clear evidence of improved economic conditions from increased agricultural
production and increased food security (El-Hajj 2010). Prior to greywater reuse, the majority of
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these households could not afford to buy irrigation water; therefore, garden productivity was
minimal (El-Hajj 2010).
Women, as the primary water managers within the home, were
encouraged to participate in the installation, use and maintenance of these greywater systems.
This participation in water governance translated to gender empowerment and improved
economic status of the women (El-Hajj 2010). This is not an isolated outcome of greywater
reuse. As noted by Hanjra et al. (2012) in a recent paper assessing global impacts of wastewater
irrigation, “peri-urban areas that use wastewater for crop production also provide employment
for women and other landless laborers,” which ultimately leads to a higher standard of living for,
and empowerment of, poorer classes of society (p. 262).
The Middle East is a particularly water challenged region of the world with some
countries relying solely on groundwater and desalination to supply water for all users. Where
most of the developed world is able to sustain water consumption rates of 7000 m3 per capita per
year, the Middle East’s freshwater resources are projected to decrease to supply rates of less than
800 m3 per capita per year by 2050 (Redwood 2010). In some Middle Eastern countries,
greywater use is estimated to be 45% of total water use (Hanjra et al. 2012). Jordan is one of the
most arid countries in the world, receiving on average less than 200 mm of rainwater per year.
Surface water resources are scarce in Jordan and groundwater aquifers supply the majority of
domestic freshwater. Currently, aquifers in Jordan are being exploited at about twice their
recharge rate (WHO-FAO 2010). Rapid population growth in refugee camps located on the
perimeter of several large cities in Jordan has led to a correspondingly sharp increase in demand
for freshwater (WHO-FAO 2010) putting these communities at risk of water shortages, food
insecurity and poor economies and unsustainable development.
As in many peri-urban
settlements, greywater irrigation of agricultural fields in a large refugee camp in Jordan is
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essential for sustaining crop production that provides the inhabitants with much needed income
and jobs (Dalahmeh and Assayed 2009). By educating local residents on proper personal and
food hygiene measures, providing sanitation programs, and using simple techniques to control
direct contact with untreated greywater, public health risks associated with greywater irrigation
were mitigated (Dalahmeh and Assayed 2009).
SUMMARY
Greywater reuse can increase both an individual household’s and community’s capacity
to grow food and provide a stable source of income in many water scarce regions of the
developing countries. At this time, additional research into soil effects, various crop uptake
capacities, soil-plant-water dynamics, and epidemiological studies evaluating true health impacts
are necessary. The current dearth of epidemiological data linking human illness with GW
irrigation of crops doesn’t mean that the risk is not real; it simply means that more targeted
studies are necessary before GW reuse can be considered completely safe. In a world where
water-borne and food borne disease continue at epidemic levels, the promotion of greywater
recycling must proceed with caution. Prohibiting or severely restricting greywater recycling is
simply impractical in many parts of the world. Direct benefits of greywater recycling include
larger agricultural production, fewer fertilizer and nutrient requirements, additional employment
and economic opportunities, and increased food security. For these reasons alone, greywater
reuse for subsurface crop irrigation and domestic purposes may prove to be essential to
sustainable development. Greywater reuse when coupled with adequate treatment technologies
and subsurface irrigation methods can provide a means of effective wastewater removal and a
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drought-resistant, constant supply of water to communities lacking access to water and sanitation
services.
For communities living in water scarce regions or in communities with no centralized
water or sanitation services, greywater recycling can provide the water needed to grow crops,
water livestock, and support economic growth. Developing resources to provide households
with appropriate GW collection, treatment, and irrigation systems in conjunction with
educational programs for users regarding system inputs and necessary hygiene measures will
help ensure that this valuable water resource does not get wasted.
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