Investigation into untreated greywater reuse practices by suburban households under the threat of intermittent water supply

Various on-site supplementary household water sources are available to residential consumers (Nel et al. 2017). In serviced areas with a reliable supply of potable water via the water distribution system (WDS), such sources may never be required – and thus may never need to be installed. A more proactive, sustainable outlook or desire to preserve water as a precious resource may, however, trigger the use of supplementary water sources. Further prompts to use supplementary sources may be out of necessity due to ongoing intermittent water supply or in an emergency situation such as a drought. Recent stringent water restrictions and news of possible water supply system failure in various municipalities in South Africa have led to increased uptake of supplementary household water sources, even in relatively affluent and well-serviced suburbs. Alternative water sources, such as rainwater (Mukheibir et al. 2014), groundwater (Wright & Jacobs 2016) and greywater (Carden et al. 2018), are commonly used in some South African cities and towns, although the penetration ratio has not yet been researched. Greywater is the least expensive and most accessible supplementary water source but poses various risks, especially when used without treatment. Untreated greywater use at the household level is the focus of this study.

Nel et al. (2017) noted that the interaction between non-potable consumer supply, such as greywater reuse, and potable municipal supply is poorly understood. There is a critical gap when it comes to an understanding of the practices regarding the relatively high-risk use of untreated greywater in serviced urban areas by residential consumers. This is an investigation into untreated greywater reuse in serviced suburban areas of the Cape Town Metropolitan area under the threat of ‘Day Zero’. It sheds light on the opportunities and challenges presented by household greywater as a consumer-driven solution to potential water supply system failure.

The metropolitan area of Cape Town is located in the South Western region of South Africa, with a population of 3.7 million people (StatsSA 2011). The city is characterised by a warm Mediterranean climate with winter rainfall and hot, dry summers. Household water consumption typically peaks in the summer months creating a demand–supply imbalance which is compounded by a heavy reliance on surface water – making up 98% of all available water sources. With dropping dam levels and relatively low rainfall, water demand was poised to outstrip supply early in 2018, but ‘Day Zero’ was ultimately avoided and water restrictions were eased in October 2018.

The focus of this study is on suburban households, where consumers are accustomed to continuous pressurised drinking water supply, with water quality in line with acceptable potable standards. Prior to the 2017/2018 drought in the study area, suburban residential consumers would generally have had no pressing need to reuse greywater, but had to consider alternative options, including untreated greywater use, when faced with the urgent and sudden dilemma of having water supply to the entire city potentially fail.

Carden et al. (2018) conducted a thorough legal review of greywater reuse in South Africa and greywater reuse guidelines for households were published (City of Cape Town 2017b) during the drought. These greywater guidelines, however, encourage greywater reuse in the interest of water saving with less emphasis on the associated risks. They are sometimes in contradiction with information in peer-reviewed journals and legislation such as the National Building Regulations and Building Standards Act (Act No. 103 of 1977), which requires that wastewater be disposed of in the sewer.

In a desperate effort to avert a major crisis with Cape Town's deepening drought, various supply augmentation and demand reduction strategies were employed; and as the drought intensified, additional behaviour changing strategies were introduced which included stringent water restrictions and increased tariffs.

Figure 1(a) and 1(b) present an overview of the water restriction levels in Cape Town and the related timelines, respectively. In June 2017, all outdoor water use in the City of Cape Town metropolitan area was banned (City of Cape Town 2017a), and the tariffs became relatively expensive with additional fines imposed on consumers for exceeding certain levels of monthly water consumption. Level 6b water restrictions were implemented in February 2018, with exorbitant tariffs and severe fines imposed on households exceeding 10 kL/month.

Despite these emergency water restrictions, Cape Town was at risk of running out of water. In January 2018, the projected date for ‘Day Zero’ was announced daily in the media, and it was defined as a day when all surface water resources combined would reach a level of 13.5% of full supply level. It was envisaged that, on ‘Day Zero’, the water supply to consumers would be closed off, with only 200 distribution points available for the physical collection of 25 L per person per day. A result of this shock tactic – and other emergency demand management measures – was that total consumption by the City of Cape Town dropped notably from 1,200 ML/day in February 2015 to 515 ML/day in March 2018 (Gosling 2018). The implementation of alternative water sources by consumers in the study area would have contributed to the notable demand reduction.

While the reduction in the potable demand is indeed a beneficial result of the ‘Day Zero’ threat, little is understood of the extent and repercussions of the uptake of these alternative water sources (including greywater).

For the purpose of this study, the term greywater is defined as all household wastewater, except toilet waste (adapted from Ludwig 1997). Greywater is inherently variable in quality, and the negative impacts on health (Christova Boal et al. 1996), the environment (Al-Hamaiedeh & Bino 2010) and water services (Penn et al. 2012) are well documented. This further highlights the need to better understand untreated greywater reuse practices during water shortages.

Past greywater studies in South Africa have focused on dense informal settlements (e.g. Carden et al. 2007) where greywater use is common due to the relatively large distances that consumers have to physically convey water from a standpipe. The informal use of greywater in unserviced areas was considered beyond the scope of this study. The focus is instead on greywater use by middle- to high-income households in fully serviced homes, during temporary yet severe water shortages.

The following were the project objectives:

• Identify a study group of greywater users.

• Design a suitable consumer questionnaire for distribution to individual consumers in the study group.

• Assess the greywater reuse practices and identify sources and end uses.

• Classify methods of collection, storage and distribution of greywater.

• Identify perceptions in terms of general risks associated with untreated greywater reuse at individual homes.

Data collection for the consumer survey occurred between 1 October 2017 and 30 August 2018, while additional analysis of online forums and social media platforms was undertaken between November 2016 and April 2017 to further determine greywater practices under the threat of ‘Day Zero’. The Water Shedding Western Cape Facebook Group provided a particularly rich source of water-saving initiatives and greywater reuse data. The group was started in January 2016 with the onset of stringent water restrictions in the Western Cape in order to share water-saving ideas online. At the time of this study, the group had 47,578 members from the greater Cape Town region.

An online survey was used due to the relatively low cost per survey and the speed with which to retrieve results, and Survey Monkey was utilised as user-friendly survey software. A link to the survey was posted with permission on institutional Facebook Pages, and further channels were utilised for the distribution of the survey. The questions were devised in line with the research objectives and the development tools as listed by Glasow (2005) so as to avoid many of the biases and disadvantages inherent in written surveys and to ensure ease of analysis. The survey included 20 questions, mostly in multiple choice format.

As the purpose of the study was to gain a general sense of greywater reuse, small sample size was deemed sufficient to gain a reasonable degree of precision (Glasow 2005). The distribution of the survey was, however, sufficient to allow for non-responses and incomplete responses (Glasow 2005).

Ethics considerations relating to confidentiality, protection of information and the informed consent process were addressed during the course of this study, and an application for ethics approval and institutional permission was accepted by Stellenbosch University in September 2017 before the distribution of the survey.

A further review of the online forum Water Shedding Western Cape was conducted to gain greater insight into the extent of greywater use. A search was conducted using keywords such as: ‘greywater’, ‘grey water’, ‘graywater’, ‘reuse’, ‘recycling’ and ‘wastewater’ in order to hone in on relevant posts. The text strings were extracted, analysed and logically organised.

The results of the survey are presented below. Respondents in the online consumer survey are referred to as Group A with forum members from Water Shedding Western Cape referred to as Group B.

The investigative online survey for Group A was completed by 175 respondents. Data were organised using Microsoft Excel, and all responses were valid and were included in the subsequent analysis. In addition, the Group B sample included another 176 forum members' posts with a total of 206 greywater-related forum posts. Ultimately, 7 different greywater generation points were identified, 12 different end uses and 3 different methods for collecting and distributing the greywater.

All respondents in Group A were located in the greater Cape Town area and were over the age of 25. Of the group, 78% resided in a suburban house serviced with potable water through a WDS. While it was not possible to determine the type of residence in which Group B members resided, it was inferred by the content of the posts including details of their appliances and plumbing systems that the majority lived in serviced homes.

The extent of greywater use in the survey sample should not be extrapolated to the larger population, because the online nature of the survey targeted respondents that have access to the internet and could create a bias towards greywater users with interest in the field.

Approximately 161 of the 175 of respondents in Group A used greywater in addition to potable water (and sometimes in addition to other alternative sources such as rainwater and groundwater) at the time of the survey.

Word clouds compiled based on words extracted from the Group A survey responses are portrayed in Figure 2 and specifically relate to sources and end uses of greywater. The main subject of these survey responses (excluding pronouns, conjunctions, adjectives, etc.) was used for the generation of the word clouds. Repeated answers were excluded, and no weighting was given. The investigation indicates that the shower was the most common source of greywater, with 87% of group A respondents utilising it at the time of the survey. The bath was utilised by 51%, while 49% utilised the washing machine, and 45% utilised the kitchen sink. Bathroom hand basins, laundry troughs and the dishwasher were utilised by a minority. The most common greywater sources in Group B included the shower (27%), washing machine (29%) and bath (20%). Less commonly used greywater sources included water from freezer defrosting, water from food preparation, geyser overflow, duck pond water replacement, and hot tub and pool backwash water.

In Group A, these greywater sources were mostly used for flushing toilets (74%) and irrigating the garden (57%). Other end uses included washing of driveways and paved surfaces, and washing of vehicles (11.5%) and bicycles (<6%).

Of Group A respondents who reused greywater for garden irrigation, the majority irrigated container plants or small sections of the garden (59%); with some watering their lawns (34%), root vegetables (4%), leafy vegetables (7%), and fruit and nut trees (11%). The results from Group B mostly included greywater reuse for garden irrigation including vegetable garden (67%) and toilet flushing (16%), and a smaller number indicated its reuse for pool filling (6%).

In Group A, 81% of the respondents distributed the greywater by carrying it in buckets to various end uses, with a further 18% indicating that piping was used for greywater distribution. The remainder utilised a dual plumbing system or a commercial product. Of the Group A respondents reusing greywater for toilet flushing, 79% were transferred directly into the cistern or toilet bowl via buckets. Analysis of the Group B forum posts indicated a fairly even distribution between makeshift, non-commercial piped systems (pumped or gravity fed) installed by the homeowner and bucketing, with a relatively minor number of group members utilising commercial greywater systems with varying levels of treatment.

Of Group A respondents, 76% reported that greywater was used without storage or was stored for less than 24 h. Storage vessels, noted in the various responses, included buckets, plastic bottles, wheelie bins etc. Of the respondents who reused greywater, 75% did not treat the greywater at all. Only 26 of the 175 respondents from Group A reported any form of treatment or disinfection, generally in the form of basic filtration and by adding bleach or other products. No respondents indicated that they used biological, chemical or other commercial systems. The use of ‘environmentally friendly’ or natural hygiene products at source was also prevalent in both Groups A and B.

A concern was identified during this study with regard to the risk of greywater use and related consumer perception of the risk. Of Group A, 71% of respondents did not perceive there to be any risk to personal health, and 57% indicated that there is no environmental risk when reusing untreated greywater.

This study probed the greywater use practices of consumers during serious water restrictions. The results paint a slim picture of actual practices standing in contrast with knowledge from published research, especially in terms of health risks inherent in untreated greywater reuse. Table 1 provides a comparison between significant Group A and B survey results and published literature:

The survey results indicate a lack of awareness of the risks of raw greywater reuse with some practices, in contradiction to the literature. Under emergency conditions, consumers are faced with a trade-off between the risks associated with reusing greywater and those associated with not using greywater (e.g. dying garden and no potable supply). Greywater reuse guideline documents highlighting the risks associated with untreated greywater use, published in the wake of ‘Day Zero’ (e.g. City of Cape Town 2017b), were ineffective in communicating the potential risks to consumers in the study sample.

Under the threat of ‘Day Zero’ and severe water restrictions, this small-scale survey in Cape Town, South Africa has given valuable insights into direct, raw greywater reuse practices.

The study highlights a lack of awareness of the significant risk to public health and the environment. It serves as a lesson to the global community facing water challenges of the complexities of conserving the potable supply, the unintended consequences and that risk laden initiatives in the interest of water-saving may prevail. The study provides insights into how individuals may respond to emergency water restrictions when given responsibility for global issues. It is a lesson in drought planning and public engagement in an increasing water stressed world.

This study has also shed light on the need for several areas of further research regarding greywater to better understand the scale of the consequential issues. This would include the effect of country wide, small-scale household greywater reuse and reduced water consumption on wastewater flows and wastewater quality in serviced areas. The legal implications of greywater mismanagement for both homeowners and water service providers are poorly understood. An examination into waterborne illnesses in the countdown to ‘Day Zero’ will also provide a better understanding of the extent of the impact greywater reuse on public health. A thorough risk assessment through the analysis and evaluation of greywater events in Cape Town or similar case studies is a further knowledge gap. It will provide a window into the vulnerability of consumers, the environment and infrastructure during drought conditions and the trade-off between risk and water-saving.