What Is Safe Sanitation?

The combination of inadequate sanitation, poor hygiene, and unsafe drinking water is responsible for 502,000 diarrheal deaths each year and millions of acute and chronic illnesses due to the fact that 2 billion people use fecally contaminated water sources (WHO 2018). Despite the fact that access to clean water and sanitation was declared a human right in July 2010 by the UN General Assembly, and despite the Millennium Development Goal (MDG) 7, Target 7.C, to “halve, by 2015, the proportion of the population without sustainable access to safe drinking water and basic sanitation” (United Nations 2010), the most recent estimates report 844 million people worldwide without access to basic drinking water service and 2.3 billion people without access to basic sanitation service (WHO and UNICEF 2017).

As of 2015, 61% of the world’s population lacked safely managed sanitation services, and approximately 85% of the world’s total wastewater is discharged without adequate or any treatment. This lack of sanitary controls combined with increasing population growth and density perpetuates the spread of infectious diseases caused by excreted pathogens, which still dominate the global disease burden in most low- and middle-income countries (Murray et al. 2012).

The world is now addressing a new set of aspiration goals, the UN Sustainable Development Goals (SDGs). Adopted in 2015, these future ambitions for human and economic development, well-being, and universal health are articulated in 17 goals that aim to reduce poverty, hunger, injustice, and pollution and increase education. SDG 6 explicitly addresses water and sanitation: Ensure Availability and Sustainable Management of Water and Sanitation for All.

The world is in dire need of investment in water and sanitation infrastructure. To reverse the deterioration of water quality, the development of innovative onsite systems, fecal sludge management, sewerage, and treatment facilities is crucial and will contribute to solving global fecal pollution; however, technology is only one piece of the puzzle. There is no doubt that environmental engineers have the knowledge to design facilities that provide improved treatment of sewage with a stated aspirational goal of moving toward resource recovery. Yet, there is no implementable roadmap to achieve such global advancements, and discussion on pathogens and the protection of public health has largely been neglected. As mentioned earlier, public health remains at risk if sanitation is not addressed. Freshwater is a key resource for human health, prosperity, and security, and therefore the protection of this resource underscores the importance of SDG 6 in improving water quality and meeting many of the other SDG targets. As communities, states, and nations move toward realizing safe sanitation, community engagement will be essential.

The question of what is safe is often asked, but no conversation for treated wastewater or fecal sludge treatment has taken place on the global stage. The authors propose that the idea of “safe” with regard to sanitation should be thought of as a social construct that lies at the intersection of knowledge, societal engagement, and controls (Fig. 1).

Continual advancement of knowledge on pathogens, hazardous substances, and chemicals in fecal wastes and wastewater is essential. Much of this knowledge depends on having the appropriate water diagnostics and laboratory capacity to study the hazards and their concentrations, which can feed into a risk assessment. Risk assessment is a tool that integrates information on the concentrations of hazards, their fate and transport throughout a system, hazardous events that increase exposure, and vulnerability factors of a population to estimate the impact of health outcomes so they can be communicated and integrated into a shared understanding of threats.

Hazards can be controlled by interventions, many of which incorporate the use of engineered technologies. Treatment technologies can adequately remove hazards (e.g., inactivate pathogens), and knowledge about their efficacy is an important component of their successful use. However, the control a person has or perceives to have over access to these technologies and interventions can also affect the person’s real and perceived safety. Control and perceived control are frequently dependent on social factors such as gender, race/ethnicity, sexual orientation, and class (Verbyla et al. 2015).

Societies around the world are defined by territory and culture. The literature in the social sciences informs us on how safety and danger are social constructs (Hollnagel 2014), often rooted in cultural beliefs about nature that are part of a person’s worldview and influence a person’s interpretation of natural phenomena. A community’s culture shapes people’s actions and reactions and the perceived cause of health outcomes. Therefore, perceived risk will vary by community and context, and an understanding of this context should influence the selection and appropriateness of interventions.

Communities need to have knowledge about risks and understand potential interventions and controls to determine where they want to be regarding safety. Thus, science and engineering knowledge transmission to the public, decision makers, and regulators is critical and must include societal engagement.

In responding to SDG 6, management strategies must include treatment of four key water pathogen groups that vary in size and their ability to survive in the environment. These include viruses, bacteria, protozoa, and helminths. Climate change is exacerbating the sewage pollution situation in that high-intensity precipitation has led to widespread flooding and transport of pathogens, posing adverse downstream risks to sanitation and treatment facilities; it is now well established that stormwater is a key factor contributing to both drinking water and recreational waterborne disease associated with fecally sourced pathogens (Curriero et al. 2001; McBride et al. 2013; Boehm et al. 2015; Jaliffier-Verne et al. 2017). The impact of large precipitation events on sewage systems needs further investigation and consideration when building infrastructure (McGinnis et al. 2018). An understanding of these temporal changes in wastewater, the discharges of fecal sludge from onsite systems to the environment, and subsequent pathogen loading to surface and ground waters will be needed as it relates to population growth and investment in future interventions.

To address the SDGs, communities will need to have knowledge about the hazards, risks, and efficacy of technology-based interventions—including their costs—in order to set meaningful goals regarding public health safety. Thus, the dissemination and translation of knowledge about pathogens within natural, engineered, and social systems is critical. To provide access to knowledge that can impact the sanitation targets in SDG 6, the Global Water Pathogen Project (GWPP) was initiated in May 2014. To date, 257 authors and editors from 46 countries have contributed 71 chapters to an online book (Rose and Jiménez-Cisneros 2019) with information on indicators of fecal pollution (6 chapters), specific human pathogens (38 chapters), and technological controls (19 chapters). The objective of the GWPP is to improve sustainable access to safe drinking water and sanitation by updating knowledge on water pathogens using advanced information technologies, publishing and disseminating a state-of-the-art open access reference work on water-related disease risks and intervention measures. This online dynamic book replaces by Feachem et al. (1983), which was originally funded by the World Bank.

Until now, Feachem et al. (1983) has been one of the only comprehensive overviews of fecal indicators and pathogen occurrence, characteristics, development, control, and dissemination in the environment. Since its publication, it has been cited as a key resource in the development of prevention strategies and guidelines for sewage-related waterborne diseases. However, its content required updating because of the dramatic increase of relevant knowledge and data over the past 35 years. The GWPP has created an online open-access database and knowledge platform that serves as a compendium of information and quantitative data on excreted pathogens to support water and sanitation safety planning, including the use of approaches based on quantitative microbial risk assessment (QMRA).

The use of risk assessment for drinking water has been endorsed in guidance documents by the WHO (2016). This discussion has addressed viruses, bacteria, and protozoa as representative pathogen groups. The global scientific consensus has suggested that safe drinking water is achieved when the annual risk of infection is less than 1 infection in 10,000 population in a year on average, or when drinking water contributes an annual disease burden that is less than 1 in 1 million (${10}^{-6}$) disability-adjusted life years (DALYs) (WHO 2016, 2017).

As an example of how this might influence the need to think about wastewater treatment as part of a multiple barrier approach, a case is presented of discharging to surface waters (Box 1) with drinking water as the final exposure. This example also uses the ${10}^{-4}$ level as the acceptable goal, although this level is further discussed in the subsequent section (“Culture, Community, and Societal Engagement”). A back-of-the-envelope QMRA calculation for the risk of ingestion of rotavirus, Campylobacter and Cryptosporidium, in drinking water and irrigation water sources that are impacted by treated wastewater (for a community that is entirely sewered) is shown in what follows. A corresponding calculation is shown for the daily and annual risks associated with drinking water sources that are impacted by fecal sludge (for a community that uses onsite sanitation systems with pit emptying). Both scenarios are addressed with the back-of-the-envelope calculations for the required overall log reduction value (LRV) for viruses, bacteria, and parasites for unplanned indirect potable wastewater reuse (Fig. 2). The impact of infection risk resulting from direct contact or from the use of nonpotable water sources for washing clothes, fishing, and recreation has not been as thoroughly addressed. There are important knowledge gaps regarding the impact of pathogens from onsite systems to groundwater sources and the impact of pathogens from biosolids derived from wastewater sludge and fecal sludge that are reused in agriculture or discharged to the environment, particularly when considering the approaches used in many low- and middle-income countries.

The following assumptions were made: 365 days of exposure per year and 2 L water consumed per person; in addition, the approximate beta-Poisson dose response model for rotavirus and Campylobacter (viral and bacterial organisms) and the exponential model for Cryptosporidium (protozoan parasite) were used. It was estimated that, in order for the annual risk to be below 1 infection per 10,000 individuals (${10}^{-4}$) per year (on average), the maximum concentration of viral, bacterial, and protozoan pathogens in drinking water (on average) should be roughly ${10}^{-7}$, ${10}^{-5}$, and ${10}^{-6}$ per liter. Chapters from Part Three of the GWPP indicate that 1 L raw sewage contains approximately ${10}^4$ fluorescent focus units of rotavirus, ${10}^7$ colony forming units of Campylobacter, and ${10}^4$ oocysts of Cryptosporidium. This means that the overall ${\log }_{10}$ reduction values for viral, bacterial, and protozoan pathogens should be 11, 12, and 10, respectively.

If a $4\text{-}{\log }_{10}$ reduction of rotavirus is provided by drinking water treatment, then a wastewater treatment plant would need to provide a $5\text{-}{\log }_{10}$ reduction, assuming a $2\text{-}{\log }_{10}$ dilution factor of effluent into the receiving waterbody (in other words, the waterbody contains 1% treated wastewater). For Campylobacter and Cryptosporidium, if $5\text{-}{\log }_{10}$ and $3\text{-}{\log }_{10}$ reductions, respectively, are achieved by drinking water treatment, and there is a $2\text{-}{\log }_{10}$ dilution factor into the receiving waterbody, then the wastewater treatment plant would also need to achieve a $5\text{-}{\log }_{10}$ reduction. While dilution in surface water is part of the calculations in this scenario, global estimates suggest that the world’s waters contain much more than 1% sewage and the ${\log }_{10}$ reductions needed cannot be achieved simply by dilution. For Cryptosporidium, for example, simulated concentrations in rivers are much higher than the required ${10}^{-6}$ per liter for drinking (Vermeulen et al. 2019). These ${\log }_{10}$ reductions may be difficult to achieve in some low- and middle-income country settings, so it may be wise to consider lower infection probabilities as intermediate health targets, as has been previously suggested for countries with high existing disease burdens (Mara et al. 2010).

The crude, back-of-the-envelope calculation shown in Fig. 2 assumes the primary exposure route is ingestion through contaminated drinking water, which, in reality, of course may not always be the main exposure route. In many cases, direct contact may be a more important exposure pathway, or in some regions, the primary use of wastewater is for agriculture. In the latter case, assuming farmers accidentally ingest $1\mathrm{mL}/\mathrm{day}$ irrigation water (Symonds et al. 2014), the same types of crude calculations (not shown) indicate that a 3- to $4\text{-}{\log }_{10}$ reduction is required to achieve a similar health target if treated wastewater were to be reused directly (i.e., no dilution) to irrigate nonedible crops or crops that are not consumed raw. This follows recommendations made previously by the WHO (2006).

Using the same assumptions stated in the example from Box 1, in order for the annual risk to be below 1 infection per 10,000 individuals (${10}^{-4}$) per year (on average), the maximum number of viral, bacterial, and protozoan pathogens in one liter of drinking water should be ${10}^{-7}$, ${10}^{-5}$, and ${10}^{-6}$ per liter. Part Three GWPP chapters indicate that one gram of feces from an infected human contains approximately ${10}^7$ fluorescent focus units of rotavirus, ${10}^9$ colony forming units of bacterial pathogens such as Campylobacter, and ${10}^7$ oocysts of Cryptosporidium. This means that the overall ${\log }_{10}$ reduction values for viral, bacterial, and protozoan pathogens should be 14, 14, and 13, respectively (Table 1).

If the incidence of a viral pathogen in a community is such that 10% of the population is excreting the pathogen, then there will be a $1\text{-}{\log }_{10}$ dilution factor associated with the feces entering onsite pits or tanks (i.e., only 10% of those feces will contain the viral pathogen). Then, assuming a $4\text{-}{\log }_{10}$ reduction of viruses is achieved by drinking water treatment, an additional order-of-magnitude reduction of risk by a vaccination program, and a dilution factor of 1 g fecal sludge into 10,000 L water, there is still a need for another $5\text{-}{\log }_{10}$ reduction, which must be achieved by a combination of onsite and centralized treatment of fecal sludge. Optimistically assuming a $1\text{-}{\log }_{10}$ reduction of viruses in an onsite system, a $4\text{-}{\log }_{10}$ reduction of viruses from fecal sludge at a centralized treatment plant would still be required. Similar calculations would indicate that the required ${\log }_{10}$ reduction values for bacterial and protozoan pathogens at a centralized fecal sludge treatment plant would be 3- and $5\text{-}{\log }_{10}$ units, respectively.

If treated fecal sludge were being used in agriculture at a rate of one part fecal sludge to nine parts soil (i.e., 10% dilution), assuming an accidental ingestion of 10 mg of soil per day by farmers, a similar type of calculation (not shown) indicates that the overall ${\log }_{10}$ reduction values for viral, bacterial, and protozoan pathogens would have to be approximately 11, 12, and 10, respectively (Table 2). This means that the required ${\log }_{10}$ reductions at a centralized fecal sludge treatment plant would need to be as high as 6 ${\log }_{10}$ units in order for the annual risk to remain below one infection per 10,000 individuals per year. This level of treatment may be difficult to achieve in some low- and middle-income country settings, indicating the need to develop more low cost, appropriate fecal sludge treatment/drying technologies, and possibly consider more modest health targets as has been previously suggested for countries with high existing disease burdens (Mara et al. 2010).

Social factors, including culture and socioeconomic status, play an important role in establishing a community’s access to safe water and sanitation (Mihelcic et al. 2017). Culture influences individuals’ perceptions about safety, which are often rooted in cultural beliefs about nature that may constitute part of a person’s worldview, which means that it influences their interpretation of natural phenomena (including the reasons why people get sick). For example, people in some communities may not perceive an infectious risk from feces of infants and as such may not dispose of them in toilets. Even if change is desired, people’s perception of control over their environment (i.e., their control over access to technology or interventions) may have a great influence on their behavior. People’s belief systems and their perception of control over their own environment may influence behaviors that affect exposure to pathogens. For example, if a community engages in point-of-use drinking water treatment and only some of the community believes that this type of treatment is necessary, then there may be little net public health benefit in terms of disease reduction in the community as a whole unless a higher level of treatment compliance is achieved by households (Enger et al. 2013).

Enger et al. (2013) found that the level of compliance or the ability to achieve a high fulfillment (95% or greater) of drinking water treatment in a community with lower ${\log }_{10}$ reductions was more important in achieving a level of safety than were higher ${\log }_{10}$ reductions of pathogens with poor coverage. The same type of analysis is needed for sanitation. In a meta-analysis of sanitation impacts on health, Garn et al. (2017) reported that, on average, the community coverage for sanitation was only 66%, with a range of 7%–100%, and only eight studies had levels above 90%. Usage was even poorer, with an average of 56%. The community must be engaged in the decision-making process, and progress toward lower risks should be the priority over a blanket recommended risk threshold. For example, achieving sanitation for all as a goal (100%) even with lower ${\log }_{10}$ reductions for pathogens and risk goals of less than 1 in 10,000 annual probability of infection, even as low as 1 in 100 should be viewed as an important pathway forward for some communities.

Achieving safe sanitation in the 21st century will require consideration of the unique challenges and needs of marginalized communities. The National Academies of Sciences, Engineering, and Medicine (2018) established five grand challenges for environmental engineering in the 21st century, the first of which is to sustainably supply food, water, and energy. The report states that these challenges require a “keen awareness of the needs of people who have historically been excluded from environmental decision making, such as those who are socioeconomically disadvantaged, members of underrepresented groups, or those otherwise marginalized” (National Academies 2018).

There is of course no one-size-fits-all solution for sustainable and effective water and sanitation services, and community stakeholders need to be involved in all steps of decision-making processes. Engagement with individuals from disadvantaged or marginalized communities as well as with professionals from multiple sectors, including engineers, water managers, microbiologists, geologists, urban planners, policymakers, and health professionals, is critical in order to choose appropriate sanitation technologies and set the appropriate goal for pathogen reduction. Policymakers face challenges finding suitable sanitation interventions because there is a lack of data on the successes and usefulness of interventions on pathogen removal and spread in the environment, in particular in developing countries. The data gaps can be immense. Even a knowledge base like the GWPP does not guarantee access to data that can be used in decision-making. To achieve “safe” sanitation, a knowledge-to-practice (K2P) initiative is needed that will explicitly engage society.

A GWPP-K2P initiative would empower water and sanitation safety planners to use an evidence-based approach to managing health outcomes by improving access to scientific data on the efficacy of sanitation technologies and the occurrence and persistence of pathogens in human waste. Visualization and use of the information are of critical importance. Scientists and engineers need to engage with stakeholders at the global, national, and local levels to work with sanitation planners on the application of existing knowledge on pathogens in sewage and human feces to sanitation planning. Pathogen emissions mapping is a key area that is expanding current knowledge related to safe sanitation (Hofstra et al. 2019). The ability to produce spatially explicit maps on the estimated loads and concentrations of waterborne pathogens emitted to waterways from sewage and fecal sludges has been used in scenario planning and risk assessment. Ultimately the advancement of such tools and training of those who need the knowledge will build the capacity of water and sanitation safety planners. The GWPP-K2P program’s audience mostly includes stakeholders from the water and health sectors who have a formal education and influence over decision-making processes at the international, national, or regional level. However, it is equally important to build capacity with a broader audience about the transmission of diseases caused by excreted pathogens to increase awareness about safe sanitation practices and behaviors. While GWPP-K2P does not specifically address this need, access to scientific data and resources is being granted, which can be a resource for water and health sector professionals who are responsible for developing culturally appropriate capacity-building programs for diverse populations, including those with little to no formal education.

The GWPP-K2P initiative has largely focused on microbial risks, given that the majority of the disease burden in less developed regions (particularly in sub-Saharan Africa) originates from communicable and infectious diseases (Murray et al. 2012). Nevertheless, the presence of other emerging chemical constituents of concern, including pharmaceuticals and personal care products and engineered nanomaterials, may also pose important threats to public health. In the future, particularly as low-income countries transition economically into emerging regions, there may also be a need to implement a K2P initiative that focuses on chemical contaminants of emerging concern.

In summary, the GWPP-K2P program can contribute to the implementation of SDG 6 on water and sanitation by the following efforts:

Table 3 shows how a GWPP-K2P platform could interface with the SDGs (Rose et al. 2019). The GWPP-K2P initiative can empower water and sanitation safety planners to use an evidence-based approach for managing health outcomes by improving access to scientific data on the efficacy of sanitation technologies and the occurrence and persistence of pathogens in sewage, fecal sludge, and environmental matrices.

http://www.waterpathogens.org/news/gwpp-water-k2p-translating-knowledge-practice-safe-sanitation.

The authors believe the following actions would move the field forward toward safe sanitation:

The K2P initiative is funded by the Bill and Melinda Gates Foundation.