Effects of long-term greywater disposal on soil: A case study

Household water use and greywater management in Khulna city, Bangladesh

While substantial progress has been made in improving water and sanitation services in low- and middle-income countries, aligned basic services such as greywater, stormwater, and solid waste management have progressed little in recent decades. Data was collected in Khulna city, Bangladesh via a household survey (n = 192) of low-income areas exploring domestic water use and greywater volumes, characteristics, and disposal practices. Most households (71%) use a piped water supply for domestic purposes, supplemented by seasonal rainwater harvesting (26%) and greywater use (13%). Of the total water used by households (mean: 594 L/household/day and equivalent to 116 L/person/day), approximately 58% becomes greywater through bathing, dishwashing, religious practices, handwashing, laundry, and mopping. Greywater produced ranges from 61-1274 L/household/day, with a mean of 345 L/household/day and equivalent to 78.4 L/person/day. Greywater characteristics vary depending on the activity, individual behaviours and any products used during cooking, bathing, or cleaning. After generation, households dispose greywater to open drains (67%), nearby waterbodies (17%) directly to the ground (9%), or decentralised wastewater treatment system (7%). Without services for greywater management, greywater disposal may have considerable public and environmental health implications, necessitating careful attention and oversight from service-providers and stakeholders beyond the household-level.

Greywater treatment in a green wall using different filter materials and hydraulic loading rates

Green walls in urban environments can be both an aesthetic feature and be of practical use in greywater treatment. This study evaluates the effect of different loading rates (4.5 l/d, 9 l/d, and 18 l/d) on the efficiency of treating actual greywater from a city district in a pilot-scale green wall with five different filter materials as substrates (biochar, pumice, hemp fiber, spent coffee grounds (SCG), and composted fiber soil (CFS)). Three cool climate plant species, Carex nigra, Juncus compressus, and Myosotis scorpioides, were chosen for the green wall. The following parameters were evaluated: biological oxygen demand (BOD), fractions of organic carbon, nutrients, indicator bacteria, surfactants, and salt. Three of the five materials investigated - biochar, pumice, and CFS - showed promising treatment efficiencies. The respective overall reduction efficiencies of BOD, total nitrogen (TN) and total phosphorus (TP) were 99%, 75%, and 57% for biochar; 96%, 58%, and 61% for pumice; and 99%, 82% and 85% for CFS. BOD was stable in the biochar filter material with effluent concentrations of 2 mg/l across all investigated loading rates. However, higher loading rates had a significantly negative effect on hemp and pumice for BOD. Interestingly, the highest loading rate (18 l/d) flowing over pumice removed the highest levels of TN (80%) and TP (86%). Biochar was the most effective material in removing indicator bacteria, with a 2.2-4.0 Log₁₀ reduction for E. coli and enterococci. SCG was the least efficient material, giving a higher BOD in the effluent than in the influent. Therefore, this study presents the potential of natural and waste-derived filter materials to treat greywater effectively and the results can contribute to the future development of nature-based greywater treatment and management practices in urban areas.

Performance of a green wall (Total Value Wall™) at high greywater loading rates and Life Cycle Impact Assessment

Nature-based greywater (GW) treatment and reuse in urban areas has become an up-and-coming option. A 14.4 m² green wall system called Total Value Wall (TVW) was installed at a terraced house in Gent (Belgium) for treating GW and reusing the effluent for toilet flushing. In a previous study, the TVW was loaded at 7 L.m^-2.d^-1 and efficiently removed TSS (67%), COD (43%), BOD₅ (83%) and total coliforms (log 2), but a number of issues were reported related to nutrient leaching from the substrate, and the excessive retention time in the storage tanks. In this study results are reported from a follow-up study during which an adapted TVW was subjected to both higher hydraulic and pollutant loading rates in order to investigate the treatment capability of TVW. The design of the system, i.e. substrate contained in geotextile bags, did not sustain the higher hydraulic loading rates as excessive leakage occurred. Despite this, the higher pollutant loading rates still resulted in an acceptable effluent quality with 15 mg.L^-1 TSS (90%), 85 mg.L^-1 COD (82%), and 15 mg.L^-1 BOD₅ (95%). Ammonium, E. coli and total coliforms were removed with removal rates of 98%, 63% (0.4 log units), and 36% (0.2 log units), respectively. Finally, a life cycle assessment (LCA) was performed for the TVW with and without treating GW to analyze the environmental burden. The LCA impacts showed that replacing tap water and chemical fertilizer by GW, and the reuse of effluent, have a positive impact. However, the energy use for pumping has a major impact and should be minimized by using an efficient pump and distribution system to reduce the overall footprint.

Occurrence of Antibiotic-Resistant Genes and Bacteria in Household Greywater Treated in Constructed Wetlands

There is a growing body of knowledge on the persistence of antibiotic-resistant genes (ARGs) and antibiotic-resistant bacteria (ARB) in greywater and greywater treatment systems such as constructed wetlands (CWs). Our research quantified ARGs (sul1, qnrS, and blaCTXM32), class one integron (intI1), and bacterial marker (16S) in four recirculating vertical flow CWs in a small community in the Negev desert, Israel, using quantitative polymerase chain reaction (qPCR). The greywater microbial community was characterized using 16S rRNA amplicon sequencing. Results show that CWs can reduce ARG in greywater by 1–3 log, depending on the gene and the quality of the raw greywater. Community sequencing results showed that the bacterial community composition was not significantly altered after treatment and that Proteobacteria, Epsilonbacteraeota, and Bacteroidetes were the most dominant phyla before and after treatment. Pseudomonas, Citrobacter, Enterobacter, and Aeromonas were the most commonly identified genera of the extended spectrum beta lactamase (ESBL) colonies. Some of the ESBL bacteria identified have been linked to clinical infections (Acinetobacter nosocomialis, Pseudomonas fulva, Pseudomonas putida, Pseudomonas monteilii, and Roseomonas cervicalis). It is important to monitor intI1 for the potential transfer of ARGs to pathogenic bacteria.

Greywater characteristics, impacts, treatment, and reclamation using adsorption processes towards the circular economy

The gap between water demand and available water supply led to wastewater treatment, particularly greywater. Due to specific characteristics of grey wastewater, treatment and recycling of this type of wastewater capture global attention. This paper presents a literature review of the remediation of greywater by adsorption processes. Besides, the reclamation of the grey wastewater in the context of the circular economy is highlighted. In this regard, the characterization of various types of grey wastewater, the potential risks associated with greywater, and the properties of reclaimed water as per the regulation or guideline are summarized. These standards vary based on the application of reused water and from a country to another country. Furthermore, this review elucidates the adsorption process in terms of the type of adsorbents, modification of adsorbents and their regeneration process, adsorption isotherm, kinetics and thermodynamic of adsorption, and optimization of adsorption system. Finally, the removal of different pollutants from greywater by various adsorbents and techno-economic aspects are illustrated.

Modelling Treated Laundry Greywater Reuse for Irrigation Using an Affordable Treatment Method and Seed Germination Test

A potential solution in areas facing water shortages is greywater (GW) reuse. GW is produced in bathrooms, laundry rooms, and kitchens of households. With proper treatment, it can be an alternative source for the agriculture sector, which consumes approximately 70% of the world’s water. This paper represents the characterization of synthetic laundry GW fraction (LGW), its treatment and modelling of treated LGW reuse for irrigation using a seed germination test. LGW’s constant quality (pH = 8.0 ± 0.3, turbidity = 174 ± 73 NTU, BOD5 = 300 ± 60 mgL−1, TOC = 162 ± 40 mgL−1) is suitable for testing the treatment method’s efficiency. Coagulation–flocculation, applying iron(III) chloride and sand filtration as a simple treatment combination, generates good-quality irrigation water (pH = 7.27 ± 0.23, turbidity = 0.6 ± 0.4 NTU, BOD5 = 17 ± 8 mgL−1, TOC = 16 ± 6 mgL−1). Seed germination tests with different waters, and elemental analysis of water, roots, and stems of the plants were done to verify the plants’ quality. The sodium adsorption ratio (SAR) for the raw LGW (SAR = 4.06) was above the threshold (<3) for safe irrigation, thus it is not recommended for this purpose. Based on the elemental analysis results and SAR value of treated LGW (SAR = 2.84), it can potentially be used for irrigation purposes.

Heavy Metals and Microbes Accumulation in Soil and Food Crops Irrigated with Wastewater and the Potential Human Health Risk: A Metadata Analysis

Wastewater is actively used for irrigation of vegetable and forage crops in arid lands due to water scarcity and cost advantages. The objective of this review was to assess the effect of wastewater (mixture sources) reuse in irrigation on soil, crop (vegetable and forage crops), animal products, and human health. The metadata analysis of 95 studies revealed that the mean of toxic heavy metals including nickel (Ni), chromium (Cr), cadmium (Cd), lead (Pb), and zinc (Zn) in untreated wastewater were higher than the world standard limits in wastewater-irrigated regions. Although heavy metals in treated wastewater were within the standard limits in those areas, the concentration of those toxic elements (Pb, Cd, Ni, Cr, and As) exceeded the allowable limits in both soil and vegetables’ edible parts. In fact, the concentration of heavy metals in vegetables’ edible parts increased by 3–9 fold when compared with those irrigated with fresh water. Escherichia coli in wastewater-irrigated soil was about 2 × 106 (CFU g−1) and about 15 (CFU g−1) in vegetables’ edible parts (leaf, bulb, tuber and fruit) while the mean total coliforms was about 1.4 × 106 and 55 (CFU g−1) in soil and vegetables’ edible parts, respectively. For human health risk assessment, the estimated daily intake (EDI) and human health risk index (HRI) ranged from 0.01 to 8 (EDI and HRI > 1.0 associated with adverse health effects). Although the mean of EDI for heavy metals from wastewater-irrigated vegetables were less than 1, the HRI for Cd and Pb were above the limits for safe consumption. Overall, heavy metal levels in wastewater that used for irrigation of agricultural crops could be within the recommended levels by the world standards, but the long-term use of this reused water will contaminate soil and crops with several toxic heavy metals leading to potential carcinogenic risks to humans. Therefore, rigorous and frequent testing (wastewater, soil, and plant) is required in cultivated farms to prevent the translocation of heavy metals in the food chain.

An Assessment of Treated Greywater Reuse in Irrigation on Growth and Protein Content of Prosopis and Albizia

This study investigated the influence of treated greywater on growth and protein content of multipurpose (forage and ornamental) transplants, Prosopis juliflora L., Prosopis tamarugo L., and Albizia lebbeck L. Transplants of tested species were irrigated with treated greywater, diluted greywater (grey + distilled water, 1:1/by volume), and distilled water (control) for seven months. Water quality analysis showed that the concentrations of nutrients and heavy metals found in the greywater were within the acceptable range compared with Jordan Institution for Standard and Metrology (JISM) and the World Health Organization (WHO) thresholds for safe use of greywater. Escherichia coli found in the greywater were lower compared to JISM and WHO guidelines for the safe use of greywater. Irrigation with treated greywater increased shoot fresh weight by 24–39% and dry weight by 34–40% compared to diluted greywater and control. No significant difference in crude protein was noticed between water treatments. Prosopis species (P. juliflora Albizia lebbeck L. and P. tamarugo Albizia lebbeck L.) had higher shoot fresh (35%) and dry weight the same species had lower crude protein (44%) when compared to Albizia lebbeck Albizia lebbeck L. The reuse of treated greywater for landscaping or forage production alleviates the demand for water resources and reduces the pressure on wastewater treatment plants. However, considering the controversial findings of previous studies on greywater quality (especially, long-term reuse), the reuse of treated greywater needs to be considered with caution and periodic quality analyses and economic assessments are required.

Domestic wastewater infiltration process in desert sandy soil and its irrigation prospect analysis

Although domestic wastewater and its reclaimed water are alternative water resources in arid region, investigation of their negative effect must be done to prevent environmental pollution. In this paper, a short-term column experiment was conducted to simulate the infiltration process of wastewater in desert soil. Alfalfa was planted and irrigated with fresh water for control (CK), tertiary treated domestic wastewater (TTW), secondary treated domestic wastewater (STW) and raw domestic wastewater untreated (RW). The effect of wastewater application on desert soil, drainage and plant properties was evaluated. Experimental results demonstrated that the tested desert soil has no soil structure, organic matter, nor microbial community while possess high infiltration rate. The use of wastewater significantly improved plant growth, and the biomass of TTW, RW, STW were 5.5, 4.3, 2.9 times of CK. The infiltration rate of water in bare soil was high (high to low: TTW, CK, RW, STW), while plant growth reduced infiltration rate (ca. 40% with TTW and RW). Wastewater irrigation and plant growth decreased soil zeta potential, while increased formation of aggregates and bacterial abundance and diversity in soil. Top soil (0-30 cm) accumulation of nitrogen (N), phosphorus (P), organic matter and E. coli was evidenced and all could go down to deep soil and drainage with constant wastewater use. It was concluded that domestic wastewater had big potential in desert soil vegetation recovering and function restoration. Nevertheless, the N, salt, P and organic matter and E. coli in wastewater could give rise to desert soil and groundwater contamination if improper treatment was used.

Assessment of water and sanitation systems at Palestinian healthcare facilities: pre- and post-COVID-19

The availability of safe drinking water and the proper management of wastewater in healthcare facilities are important pillars for maintaining safety of workers, patients, and visitors and protecting human health and environment. Water and sanitation services at 495 healthcare facilities in the West Bank of Palestine are assessed using the results of PCBS and MoH (2014) survey study. Services are reassessed after the COVID-10 pandemic using personal interviews with experts from healthcare facilities, regulatory authorities, and service providers. The results show that 92.1% of healthcare facilities were connected to public water networks, 12.9% of them purchased water tanks, and 10.8% of them depended on harvested rainwater which may cause contamination and waterborne diseases. Regardless the source of freshwater, the water quality has to be regularly examined and compared to local guidelines and international standards for health promotion. Almost 63.4% of healthcare facilities were not connected to wastewater networks and used either tight or porous cesspits. Once these cesspits are filled off, wastewater is randomly disposed into nearby valleys causing adverse environmental impacts on air, water, and land resources. Medical wastewater of hazardous substances should be treated before discharged to wastewater networks. Experts assured that although heightened procedures have been made by service providers to curb the spread of the COVID-19 disease, yet, more consistent protocols and stringent procedures are crucial. There have not been any new directives or procedures regarding the management of water supplies and wastewater services in the healthcare facilities. Stakeholder collaboration can help prevent the COVID-19 disease.

What is the impact of personal care products selection on greywater characteristics and reuse?

Accounting for up to three quarters of the wastewater volume resulting from domestic activities but containing only a third of its organic content, greywater is seen as an alternative water source for non-potable reuse. This unique study explores the question whether consumers' product selection could affect the treatability and reuse of bathroom greywater. Fifty five personal care and household products (PCHP) were analysed for their effects on a range of water quality parameters including their aquatic and soil toxicity using Microtox® and MicroResp™. The organic content of these PCHPs varied considerably, not only from one category to another (0.2 g_TOC.L^-1 for hair conditioners to 2.7 g_TOC.L^-1 for toothpastes), but also within each category (0.1 g_TOC.L^-1 to 3.6 g_TOC.L^-1 amongst the shampoos). As expected, the PCHPs' macronutrient content was low, suggesting some limitation towards biological treatment of bathroom greywater. Regarding the impact of product selection on toxicity towards aquatic and soil microorganisms, the results revealed a higher sensitivity of Vibrio fischeri to the individual PCHPs than the MicroResp™ soil microorganisms. In the latter case, 75% of the products caused a stimulation response from the microorganisms although some decreases in basal respiration were observed for specific PCHPs within product categories. However, based solely on MicroResp™, the short-term discharge of treated bathroom greywater, regardless of consumer product selection, is unlikely to have a negative impact on soil microbial activity. Overall, the work has demonstrated the importance of consumer choice on the pollution load and treatability of greywater. However, no clear link between greywater characteristics and factors that normally determine consumer product selection (branding, type) were identified. This means it is not currently possible for consumers to actively manage the issue through choice such that process designers and technology developers must ensure technologies are sufficiently robust to manage the potential variations that could occur.

Quantifying the Benefits of Residential Greywater Reuse

There is paucity of data on the quantification of the benefits of residential greywater reuse via direct diversion. While estimates have been made based on modelling the potential mains water savings, it is also recognised that the practicalities of system operation and occupant behaviour introduce substantial variation to these estimates. Three single residential housing projects in Fremantle, Western Australia, undertaken over ten years with a substantial focus on water efficiency and mains water substitution, have provided an opportunity to quantify these benefits. All three dwellings were intensively metered and documented. This paper describes the learnings generated along the way, including the methodology developed to effectively integrate direct diversion greywater reuse into a productive garden, along with other water sources to satisfy landscape water demand. Importantly a robust quantification of actual greywater volumes and associated mains water savings was made. The publication of actual greywater volumes will significantly contribute to this field and go a long way towards validating the merits of residential greywater reuse on mains water savings when systems are properly installed and operated. Brief considerations are also provided for energy efficiency and financial assessment.

Reasons of Acceptance and Barriers of House Onsite Greywater Treatment and Reuse in Palestinian Rural Areas

In the last twenty years, house onsite wastewater management systems have been increasing in the West Bank’s rural areas. The aim of this research was to reveal, in the context of providing onsite Grey Water Treatment Plants (GWTPs) for wastewater management in the rural communities in Palestine, the local population’s perceptions, in the sense of acceptance of and barriers towards such a type of wastewater management, so as to figure out successes, failures and lessons. The data collection tool was a questionnaire that targeted the households served with GWTPs. The findings show that 13% of the total constructed treatment plants were not operative. The most important barrier as mentioned by 66.5% is odor emission and insect infestation. Then, 25.1% of the implementing agencies never monitor or check the treatment plants, and 59.3% of them monitor and check the plants only during the first 2–3 months. The next barrier is inadequate beneficiary experience in operation and maintenance. Health concerns regarding quality of crops irrigated by treated grey water were another barrier. The results revealed that the reuse of treated grey water in irrigation was the main incentive for GWTPs as stated by 88.0% of beneficiaries. The second incentive was the saving of cesspit discharge frequency and its financial consequences, as stated by 71.3%. Finally, 72.5% of the beneficiaries stated that they had a water shortage before implementing GWTPs, and the GWTPs contributed to solving it. The highest percentage (82.6%) of beneficiaries accepted the treatment units because of their willingness to reuse treated water for irrigation and agricultural purposes. Education level has an impact on GWTP acceptance, with 73% of not educated beneficiaries being satisfied and 58.8% of educated people being satisfied. Islamic religion is considered a driver for accepting reuse of treated grey water in irrigation, according to the majority of people (70%). Women play a major role on GWTP management; 68.9% of the treatment systems are run by men side-by-side with women (fathers and mothers), and 24% are run completely by women. The majority of GWTP beneficiaries (70.4%) are satisfied with GWTPs. Little effort is required for operation and maintenance, with only an average of 0.4 working hours per week. Therefore, house onsite grey water management systems are acceptable in rural communities, but attention should be given to the reasons of acceptance and barriers highlighted in this research.

Hospital discharges in urban sanitation systems: Long-term monitoring of wastewater resistome and microbiota in relationship to their eco-exposome

Wastewaters (WW) are important sources for the dissemination of antimicrobial resistance (AMR) into the environment. Hospital WW (HWW) contain higher loads of micro-pollutants and AMR markers than urban WW (UWW). Little is known about the long-term dynamics of H and U WW and the impact of their joined treatment on the general burden of AMR. Here, we characterized the resistome, microbiota and eco-exposome signature of 126 H and U WW samples treated separately for three years, and then mixed, over one year. Multi-variate analysis and machine learning revealed a robust signature for each WW with no significant variation over time before mixing, and once mixed, both WW closely resembled Urban signatures. We demonstrated a significant impact of pharmaceuticals and surfactants on the resistome and microbiota of H and U WW. Our results present considerable targets for AMR related risk assessment of WW.

Greywater recycling in buildings using living walls and green roofs: A review of the applicability and challenges

Living walls and green roofs offer numerous benefits to densely populated urban areas such as cooling, air filtering and improved aesthetics. However, plants in these two systems are high water consumers making such systems particularly unsuitable for water-scarce arid environments most at need of passive cooling and urban greening. Integrated greywater treatment in these structures provides a possible solution, providing plants not only with water but other required nutrients and organics. However, greywater treatment by living wall and green roof systems is still lacking. This review summarizes the few studies exploring this new integrated technology and provides an in-depth analysis of existing literature on vegetated building structures and greywater treatment to reveal benefits and potential pitfalls of this technology. Appropriate selection of plants and media are essential to successful system design and must meet competing demands compared to those used in existing vegetated building structures for cooling/greening and constructed wetlands for greywater treatment. A variety of operational and user-interaction issues are also explored and will be key areas of future research to enable full-scale implementation. Integrated greywater treatment using green building vegetated structures appears a promising method for dual purpose water recycling and urban cooling, and various future research needs are emphasized to realize this.

Greywater characterization and generation rates in a peri urban municipality of a developing country

The quantity and quality of combined greywater from houses with in-house water supply and houses that rely on external sources of a peri-urban area in a developing country were determined. Data for quantity of greywater was collected from 36 households while 180 samples of greywater were collected from 60 households between December 2016 and February 2017. The results indicate that, average water consumption from households with in-house access was 82.51 ± 12.21 Lc^-1d^-1 while households which rely on external sources was 36.64 ± 4.31 Lc^-1d^-1 with return factors of 74.16% and 88.57% respectively. Quality analysis also showed significant differences between greywater from the two sources with most of the quality parameters exceeding the regulatory limit. The ratio between biochemical oxygen demand (BOD₅) and chemical oxygen demand (COD) ranged between 0.22 and 0.59 for greywater from in-house sources and 0.23-0.62 for external sources indicating low biodegradability of the greywater. The nutrients recorded exceeded the trigger levels for eutrophication while significant levels of microorganisms such as E. Coli and Salmonella spp. were also detected in both streams. Direct reuse of greywater for irrigation was found to be unsuitable based on the salinity and sodium hazard analysis. Principal component analysis of the data indicated that the characteristics of the combined greywater in the study area is influenced by cooking and cleaning practices, personal hygiene, biodegradability, frequency of water use before disposal and sanitary practices in the bathroom. The greywater discharged is detrimental to the environment and poses a health risk to humans and livestock. There is therefore the need for authorities involved to prioritize greywater management and treatment in peri-urban areas of developing countries.

Development of groundwater vulnerability zones in a data-scarce eogenetic karst area using Head-Guided Zonation and particle-tracking simulation methods

Delineation of groundwater vulnerability zones based on a valid groundwater model is crucial towards an accurate design of management strategies. However, limited data often restrain the development of a robust groundwater model. This study presents a methodology to develop groundwater vulnerability zones in a data-scarce area. The Head-Guided Zonation (HGZ) method was applied on the recharge area of Oemau Spring in Rote Island, Indonesia, which is under potential risk of contamination from rapid land use changes. In this method the model domain is divided into zones of piecewise constant into which the values of subsurface properties are assigned in the parameterisation step. Using reverse particle-tracking simulation on the calibrated and validated groundwater model, the simulation results (travel time and pathline trajectory) were combined with the potential groundwater contamination risk from human activities (land use type and current practice) to develop three vulnerability zones. The corresponding preventive management strategies were proposed to protect the spring from contamination and to ensure provision of safe and good quality water from the spring.

Greywater-induced soil hydrophobicity

Greywater (GW) reuse for irrigation is a common method of reducing domestic consumption of fresh water. Most of the scientific research and legislation efforts have focused on GW's health risks, while less attention has been given to its environmental outcomes. One of the environmental risks of GW irrigation is its possible effect on soil hydraulic properties. This research examined the ability of GW to induce soil hydrophobicity, as well as its degree and persistence. Fresh water (control) and three model GW solutions representing raw, treated and highly treated GW were used to wet fine-grained sand. Every treatment was subjected to five cycles of wetting, incubation (at 5 °C or 30 °C) and drying (60 °C). After each cycle, capillary rise was measured and the contact angle (CA) was calculated. Samples were also tested by the Wilhelmy plate method to retrieve advancing and receding CA and reservoir surface tension. Water repellence of the sand, as implied from the CA, increased with increasing GW concentration and was highest in the sand coated with the model raw GW and incubated at 5 °C. However, none of the treatments resulted in what is considered to be "water-repellent soil". Furthermore, when raw GW-coated sand was immersed in water, its surface tension was significantly reduced relative to the other treatments, implying a release of surface-active compounds from the sand into the water. It was postulated that untreated GW may induce sub-critical water repellence in sand. However, this effect is sensitive to biodegradation and washing processes and is therefore temporary.

Potential microbial hazards from graywater reuse and associated matrices: A review

Millions of decentralized graywater-reuse systems are operating worldwide. This water is directly accessible to household inhabitants, raising environmental and public health concerns. Graywater may contain a variety of harmful organisms, the types and numbers of which vary with source-type, storage time, and background levels of infection in the community source. In this review, we find that most studies indicate high amounts of microbial pathogens in raw graywater and therefore treatment and disinfection are recommended to lower possible health risks. Where these recommendations have been followed, epidemiological and quantitative microbial risk-assessment studies have found negligible health risks of bacterial pathogens in treated graywater. Chlorine is currently suggested as the most cost-effective disinfection agent for inactivating graywater bacterial pathogens and preventing regrowth. Various studies demonstrate that the introduction and diversity of pathogenic bacteria in the soil via irrigation can be affected by several factors, but treated graywater may not be a major contributor of bacterial contamination or antibiotic resistance. However, an accurate assessment of the infectious capabilities, exposure pathways, and resistance of specific pathogens, particularly viruses and antibiotic-resistant bacteria found in treated graywater after disinfection, as well as in the graywater piping, irrigated soils, plants, and associated aerosols is largely lacking in the literature. In addition, research shows that fecal bacterial indicators might not reliably indicate the presence or quantities of pathogens in graywater and thus, the indicator standard for graywater contamination should be revised.