Adverse health outcomes associated with onsite sanitation, the system by which household wastewater is partially treated without conveyance to centralized wastewater treatment systems (CWTSs), are commonly thought of as an issue in low- and middle-income countries, and not one that would impact those in the United States. Research about onsite sanitation in the United States has increased significantly in the past decade, and this misconception is finally being revisited. As recently as 2011, some even felt comfortable claiming that “indoor plumbing and sanitation are taken for granted in developed countries,” (Hartley and Van Meter, 2011) including the United States, and that households lacking access to CWTSs “are nonetheless able to rely on clean water … and utilize onsite sewage facilities such as septic tanks for sanitation” (Hartley and Van Meter, 2011). But sanitation cannot be taken for granted by many in the United States, where households using onsite wastewater treatment systems (OWTSs) may still lack access to safely managed or even basic sanitation.

The WHO/UNICEF Joint Monitoring Programme (JMP) defines basic sanitation as the “use of improved facilities that are not shared with other households,” (Sanitation) where improved facilities are classified as those which are “designed to hygienically separate excreta from human contact” (Sanitation). To move from basic to safely managed sanitation, a facility must further ensure that “excreta are safely disposed of in situ or removed and treated offsite” (Sanitation). The authors use the terms “safe sanitation” and “unsafe sanitation” for any situation in which the definition for safely managed sanitation is met or not met, respectively. Data on 2020 Sustainable Development Goal indicate that over 5.75 million individuals (1.74 % of the population) lack access to a safely managed sanitation facility (Goal 6, 2023). This represents a pressing human rights issue as well as a major economic burden, “costing the US economy $8.58 billion each year” (Draining). Further analysis estimates that 930,000 individuals residing in the urban United States “lacked sustained access to at least basic sanitation” (Capone et al., 2020).

Sanitation is provided to more than 75 % of U.S. households through CWTSs operated by municipalities (Septic Systems, 2015). The remaining percentage of households may lack access to municipal sewer services due to distance of household to nearest sanitary sewer main or intractable topographical conditions (Septic Systems, 2015). In addition to physical factors impacting CWTS access, there are many social, political, and economic determinants that are often overlooked. Many marginalized communities, including low-income urban neighborhoods and those in rural areas, who do not have access to CWTSs. Further, socio-cultural factors and systemic inequalities contribute to inaccessibility to CWTS among specific demographic groups.

These communities lacking access to CWTS rely on decentralized sanitation technologies via OWTSs. In the United States, the vast majority of OWTSs are septic systems, which utilize a water-tight chamber and a drainfield. When functioning properly, a septic tank will receive household wastewater, allowing for heavy solids to settle at the tank bottom and sometimes be anaerobically digested. Greases, light solids, and septic tank effluent are then “discharged to the drainfield for further treatment and dispersal” (Types of Septic Systems, 2018).

Septic systems can provide safe sanitation to their users. However, when they malfunction or fail, they can expose households and those in the surrounding area to a variety of dangerous pathogens, including campylobacter, giardia spp., salmonella spp., shigella spp., (Diseases Involving Sewage, 2021) and hookworm (McKenna et al., 2017) via consumption of contaminated well water or through contact with contaminated water or soil. Septic systems can fail at relatively high rates. Studies have found evidence of hydraulic failure in 35 % of households reliant on septic systems with drainfields in one Alabama community (Maxcy-Brown et al., 2021; White, 2022), and of “septic system failure rates of 50–100 % on several streets” (Wilson et al., 2008) in a North Carolina community. Septic systems can fail for many reasons, including “structural failure, improper siting, poor construction, lack of maintenance, or changes in environmental conditions” (Hoghooghi et al., 2021). Likelihood of failures can also be influenced by construction type of drainfield, type of surrounding soils, groundwater/water table level, number of bedrooms in the household, and frequency of flooding (Hoghooghi et al., 2021). When failing septic systems are not repaired or replaced, nearby residents may experience chronic exposure to pathogens and potentially toxic levels of nutrients (Hoghooghi et al., 2021). Outbreaks of excreta-related disease, such as that of hookworm in rural Alabama (Pilkington, 2017), are potential resultant adverse health outcomes of such exposure.

On a global level, similar challenges are observed, particularly in low-income communities where most people use OWTS (Dasgupta et al., 2021). Limited resources, poor infrastructure, and lack of education perpetuate barriers to safe sanitation. This is further exacerbated by poverty, population density, and insufficient government investment which can collectively impede access to clean and safe sanitation facilities, amplifying health hazards and hindering socioeconomic development (Fewtrell et al., 2005). Despite variations in scale and context, shared obstacles to safe sanitation among housed populations in the United States and worldwide underscore the urgent need for comprehensive strategies addressing infrastructure, socioeconomic disparities, and educational initiatives to ensure equitable access to essential sanitation services for all.

No social, economic, or political interventions and policy-changes can fully address the prevalence of unsafe sanitation in the United States before the many complex barriers that contribute to the problem are understood. Since the advent of ubiquitous sanitation technologies in the United States, there has never been a more pressing time to map these barriers and act to eliminate them. Many publications have described access to water and sanitation in the United States but are subject to limitations, such as incomplete coverage of the entire country or little to no discussion on the diverse barriers impeding access to sanitation. For instance, Capone et al. (2020) offers an excellent overview of populations lacking access to full and safe sanitation in urban US communities but does not include extensive information on barriers to access, nor does it explore rural communities. A review by Mueller and Gasteyer (2021) draws attention to the extensive drinking water inequities throughout the country but does not focus on sanitation. Izenberg et al. (2013) included in this review, provides thorough commentary on barriers to sanitation in Alabama's Black Belt but not for areas outside of this region. Given the crucial role of proper sanitation to public health and well-being, it is imperative to identify the various socio-cultural, economic, and political factors that influence access to safe sanitation and their interplay. Understanding these dynamics is essential not only for identifying the existing challenges but also for formulating effective and inclusive solutions that address the diverse needs of different communities in the United States.

To the authors' knowledge, this paper provides the first systematic review of the barriers to safe sanitation throughout the entire United States among housed populations. Furthermore, this review describes the contributing social determinants. The review also illustrates why the responsibility for obtaining and maintaining safe sanitation in the United States (and globally) should not fall solely on residents. This review explores several barriers, including current and historical factors affecting a community's annexation or incorporation status, socioeconomic status, availability of public funding, land tenure, rurality, and distrust in authority. Hydroclimatic and geological risks that contribute to system failure or installation and maintenance challenges are discussed in reference to these barriers. Note that challenging geological conditions are not, by themselves, causative agents of unsafe sanitation. Also note that every community experiences a different set of barriers that impact their access to safe sanitation, and thus require a unique set of solutions. Thus, this review presents the barriers to safe sanitation found in some communities around the United States and that should be considered when evaluating and understanding sanitation. By providing information on the nuanced relationships between sanitation access and broader societal elements, our review may inform policies and initiatives toward improved sanitation infrastructure and practices, thereby contributing to the overall well-being and development of communities not only within the United States but also in various regions around the world.