Introduction

The concept of transformative water, sanitation, and hygiene (WASH) states that the complete removal of fecal contamination from the household environment is necessary to improve health outcomes1. India’s government has helped millions of households make progress towards this goal over the past few years through Swachh Bharat Abhiyan and the Jal Jeevan Mission, programs designed to increase household-level access to toilets and piped water, respectively. As of 2022, 86% of households in India had a working tap connection thanks to Jal Jeevan while the prevalence of households without a toilet had fallen to below 18%2,3. Households with access to improved toilets and piped water are less likely to be exposed to fecal contamination4,5.

How wastewater streams are contained and conveyed to treatment facilities is also critical to reducing fecal contamination inside the home. For example, as of 2021, approximately 7.1% of individuals in India were using toilets connected to a piped sewer network2. Most Indians with a toilet, however, rely on some form of on-site containment. Almost 75% of individuals in India had a toilet that either flushed to a septic tank, flushed to a pit, or used a pit or dry toilet, and the majority of the remaining 18% of individuals did not have a toilet2. These homes have to rely on something other than piped sewers for conveying waste to a treatment facility. Historically, this was done manually in India. This practice was rightfully outlawed in 2013 as a part of the Prohibition of Employment as Manual Scavengers and their Rehabilitation Act6. This legal shift underscored the need for mechanized methods of waste conveyance, such as trucks with pumps and hoses. These tanker trucks, which are either provided by municipalities or operated by private enterprises, can be used by households to empty these containers before they overflow7.

However, the supply of tanker trucks has not kept up with burgeoning demand for waste conveyance brought about by increased household toilet and piped water coverage throughout India7. Thus, septic tanks and soak pits often overflow into drains5, which in many cases are open to the environment. The flow of untreated waste through open drains can be hazardous to health in a number of ways8,9. People are at a greater risk of ingesting contaminated water and are at a greater risk of making dermal contact with pathogens if waste flows in open drains10. This is a major cause of infectious disease in the Indian context11. These open drains can flood during heavy rains, which is associated with the spread of enteric infections among children12. Open drainage is also associated with an increased risk of acute respiratory illness13, and cholera outbreaks14,15.

The prevalence of drainage types available to households has been studied in prior surveys conducted in India. For instance, the 76th round of India’s National Sample Survey (NSS) from 2018 focused on drinking water, sanitation, hygiene, and housing conditions, and contains data on the type of drainage available to households16. Results from this survey show that over 33% of households were relying on open drainage, and over 28% of households had no drainage16. Only 26.7% of households at the time of this survey had access to an underground drainage system16.

Now, the fifth round of India’s National Family Health Survey (NFHS-5), which concluded in 2021, allows for updated estimates on the prevalence of household drainage. Updating these estimates is important for several reasons. Like the 76th round of the NSS, NFHS-5 was designed to be nationally representative, and contains data from all 36 states and Union Territories16. But, while the 76th round of the NSS had data from 106,838 households16, NFHS-5 contains data from 636,699 households17. NFHS-5 data can be used to provide updated national estimates on the prevalence of drainage types from a much larger sample. This is crucial given that as of 2021, almost 60% of homes in India rely on either a pit or septic tank17. Furthermore, India’s district geometry changed between 2018 and 2021. Thus, NFHS-5 can also be used to elucidate the geographic variation in drainage types between a more current set of districts, something which has not been done before. Doing so is critical given that Sustainable Development Goal 6 calls for the availability and sustainable management of water and sanitation for all18.

Therefore, the purpose of this paper is to use these data to elucidate the prevalence of drainage types across 720 districts in India and by urbanicity as way to understand the geographic distribution of drainage throughout the country. The focus on districts is important given that this is the unit of administration at which national and state policies are implemented and carried out19. Next, we examine the type of drainage coverage by household toilet and water access. Finally, we examine household drainage type by household wealth, education, and caste. These analyses are important to identify and prioritize geographically and socioeconomically vulnerable populations that require interventions to keep waste streams separate from human contact to promote positive health outcomes.

Results and discussion

Sample characteristics

Approximately 20% of the individuals in the study sample lived in each of the five household wealth quintiles (lowest, low, middle, high, and highest). Among the 636,699 heads of households who responded to the survey, approximately 28.5% had no education (zero years of schooling), 18.6% had a primary education (one to five years of schooling), 42.0% had a secondary education (six to 12 years of schooling), and 10.9% had a higher education (above 12 years of schooling). Approximately 66.8% of the NFHS-5 sample lived in a rural area, and almost 33.2% lived in urban areas. Approximately 4.7% of the sample reported having no caste while 0.9% reported not knowing their caste. Approximately 21.7% of the sample belonged to a Scheduled Caste, 9.5% belonged to a Scheduled Tribe, 41.6% belonged to a Other Backwards Caste, and 21.6% reported belonging to some other caste. The representation of caste groups in the NFHS is consistent with what has been reported in other nationally representative surveys from India20. These results are reported in Table 1.

Table 1 Description of the characteristics of the sample included for analysis
Full size table

Geographic distribution of drainage types

The all-India prevalence of no drainage was 24.7% (95% CI: 24.6–24.8), and the all-India prevalence of open drainage was 37.5% (95% CI: 37.3–37.6). The all-India prevalence of drains to soak pits was 3.8% (95% CI: 3.7–3.9). Finally, the all-India prevalence of closed drainage was 33.9% (95% CI: 33.7–34.0).

The all-India median district-level prevalence for no drainage was 22.4% and the interquartile range (IQR) was 28.2 percentage points. The all-India median district-level prevalence for open drainage was 42.5%, and the IQR was 24.3 percentage points. The all-India median district-level prevalence for drains to soak pit was 2.6% with an interquartile range (IQR) of 4.1 percentage points. Finally, the all-India median district-level prevalence of closed drainage was 24.4% with an IQR of 28.1 percentage points. These results are presented in Figs. 1 and 2, and in Supplementary Tables 2, 3 and 4.

Fig. 1
figure 1

District-level distribution of prevalence (%) for no drainage, open drainage, soak pit, and closed drainage at the all-India level, 2021. The upper and lower whiskers represent minimum and maximum values, respectively. The upper outline of the box depicts the 75th percentile and the lower outline the 25th percentile. The solid line within the box shows the median (50th percentile).

Full size image
Fig. 2: District-level prevalence of drainage types throughout India in 2021.
figure 2

A No drainage B Open drainage C Soak pit D Closed drainage.

Full size image

The median district-level prevalence for no drainage was 28.0% in rural communities versus 6.8% in urban communities. Likewise, the median district-level prevalence values for open drainage and drains to soak pits was higher in rural communities than in urban communities. However, the median district-level prevalence for closed drainage was 46.1% in urban communities versus 17.2% in rural communities. The IQR values for closed and open drainage were higher in urban communities than in rural communities. This points to a greater degree of inequality in these two drainage types in urban communities. The IQR values for drains to soak pits and no drainage were higher in rural communities than urban communities. These results are presented in Supplementary Figs. 1 and 2.

Relationship between types of drainage

Overall, there were moderate negative correlations between the all-India district-level prevalence values for each of the drainage types. The only exception to this was a small positive correlation between the all-India district-level prevalence values for no drainage and soak pits (r = 0.11, p < 0.01). The same patterns were observed across urban and rural communities as well.

Relationship between drainage types and household water and toilet access

At the all-India level, 41% of households with an improved toilet had access to closed drainage. Conversely, 39% of households without an improved toilet relied on open drainage, and 26% had no drainage. Urban households with improved toilets were more likely to have closed drainage than rural households with improved toilets. However, rural households with improved toilets were more likely to have open drains or no drainage than urban households with improved toilets. These results are presented in Fig. 3 and Supplementary Table 1.

Fig. 3: Percent prevalence of drainage types at the all-India, rural, and urban levels.
figure 3

A By household toilet type B By household water source.

Full size image

At the all-India level, 40% of households with piped water access had closed drains and another 40% of those with piped water relied on open drainage while 17% of people with piped water had no drainage. Urban households with piped water were more likely to have closed drainage than rural households with piped water. However, rural households with piped water were more likely to have either open drains or no drainage than urban households with piped water. These results are presented in Fig. 3 and Supplementary Table 1.

Socioeconomic correlates of drainage type

Overall, we found that individuals in the lowest socioeconomic groups were most likely to live in homes that relied on no drainage or open drains. Those in the highest socioeconomic groups were most likely to live in homes with closed drains. We did not find a meaningful socioeconomic gradient in the context of drains to soak pits. These patterns were true for household wealth quintile, the highest education of the household head, and caste. These results are presented in Table 2.

Table 2 Prevalence of drainage type by socioeconomic status, 2021 for all 636,699 households
Full size table

The purpose of this study was to elucidate the prevalence of drainage types at the all-India level, across 720 districts in India, by household toilet and water access, and by household wealth, education, and caste. We found that open drainage is the most common form of drainage throughout India followed by closed drainage. The household prevalence of open drainage was above 42% in more than half of India’s 720 districts. Similarly, the household prevalence of closed drainage was below 24% in more than half of India’s 720 districts. Second, open drains and no drainage were more common in rural communities than urban ones. The inverse was true for closed drainage. Third, households with an improved toilet were more likely to have closed drainage or drainage to a soak pit than households with an unimproved toilet. But, households without an improved toilet were more likely to have either open drainage or no drainage than households with an improved toilet. Households with piped water access were more likely to have closed drainage than those without piped water access. Finally, India’s lowest socioeconomic households were most likely to rely on open drains or no drainage, while those in the highest socioeconomic groups were the most likely to have access to closed drains.

There are a few data limitations associated with this study. First, while the type of drainage households have access to might be known, the waste streams flowing through these drains is unknown. There was one exception to this as NFHS-5 participants were asked where they dispose of kitchen waste and open and closed drains were response options. However, the fact that people rely on an open drain does not necessarily mean that they are being exposed to hazardous waste. Second, the NFHS-5 does not ask people that have toilets with septic tanks or soak pits whether they utilize a mechanized system for waste removal and conveyance. Therefore, the extent to which a toilet is at risk for overflowing is unknown. Third, there is no information provided on where waste streams flow when households report having no drainage. This means that there is no information on the extent to which local water bodies, surface or underground, might be polluted. Fourth, while the NFHS-5 does ask whether the toilet is connected to a piped sewer network, the NFHS-5 does not contain any data on whether a drain leads to a piped sewer network. Thus, regardless of drain type, we do not know if the waste flows are being properly treated. Finally, we included 26 districts from Andhra Pradesh even though the original dataset only included information from 13 districts. Thus, it is possible that the results from these districts are underpowered. However, the standard errors (presented in the supplementary tables) suggest that the prevalence estimates for these districts are precise.

These findings underscore the extent to which the idea of transformative WASH remains an aspirational goal. Drainage systems play a vital role in removing fecal contamination from the home, a key goal of transformative WASH1, connecting wastewater flows from homes and communities to treatment facilities. Approximately a third of Indians have access to a closed drain, mitigating their exposure to hazardous waste flows. However, whether the waste conveyed by these closed drains is being treated is unknown. For example, data from the Government of India show that less than 28% of India’s sewage is currently being treated21. This suggests that waste flows are likely being discharged, untreated, into local water bodies10, putting people at risk for disease. Future research should examine the extent to which drains – of any type – are properly conveying waste streams to sewerage treatment plants or if they are releasing elsewhere. Additionally, the proportion of Indians with an improved toilet has also risen considerably over the past decade2. This has helped prevent open defecation, thereby limiting people’s exposure to fecal excrement. Yet almost 37% of homes with an improved toilet rely on an open drain, something that could counteract or undermine the potential health gains of improved toilet access. This study also shows that almost a quarter of Indians live in homes with no drainage. This can allow for fecal contamination to more easily disperse22, which could be associated with an increased risk of diarrhea especially during periods of heavy rain fall23. This finding points to the importance of scaling up the provision of tanker trucks and other mechanized methods of removing waste so that the waste from homes without drains is properly conveyed to treatment facilities. Thus, this study highlights that the availability of adequate drainage systems, a topic that has been understudied to date, must be considered as a part of future WASH interventions that hope to remove untreated fecal contamination from the environment.

The findings from this study also underscore the importance of examining place-based disparities in public health infrastructure. Nationally, the prevalence of open drainage was just below 40%. However, the prevalence of open drainage was above 42% in most of India’s 720 districts, and open drainage was more common in rural communities than urban ones. Similar patterns were observed with closed drainage as the national average was almost 34% but was less than 24% in most of India’s districts. When looking at the urban-rural divide, urban residents were far more likely to have access to closed drains than rural residents. Again, this mirrors the urban-rural divide with regards to water and sanitation access24. These disparities can be explained in part by the idea of remoteness. More specifically, O’Reilly et al. show that the structural inequalities that contribute to lower rates of toilet coverage in rural areas are exacerbated by the fact that rural residents are further, both physically and socially, from decision makers25. Rural residents who participated in another qualitative study in India describe feeling left behind by policy makers, who they say focus their efforts on big cities and “big people”26. The findings from this study are consistent with these prior results in that they show how critical water and sanitation infrastructure—closed drainage in this case—is more common in urban areas. Infrastructure development is also more costly in rural areas, making India’s rural poor “expensive to deal with”, yet another possible explanation as to why proper drainage has not been prioritized in India’s rural communities27.

The results show, for the first time, that those in India’s lowest socioeconomic groups are most likely to rely on open drainage or no drainage. This finding further underscores the extent to which India’s most marginalized are often subjected to poor environmental health conditions. For instance, previous work demonstrates that India’s least socioeconomic advantaged household often do not have access to clean cooking fuel28,29, private toilets26, and clean drinking water30,31. Similarly, this study shows that those in the lowest wealth quintile, those who had no education, and those who belong to a historically marginalized caste were most likely to have open or no drainage. Exposure to inadequate drainage is yet another pathway that underscores the relationship between poverty and morbidity. Thus, in addition to targeting geographic regions that are more likely to have open or no drainage, policy makers must also target those who are most socioeconomically disadvantaged.

In conclusion, open drainage is prevalent throughout India, especially in rural areas and among India’s most socioeconomically disadvantaged groups. Those who have access to closed drains tend to live in urban communities, and tend to be wealthier, more educated, and from a higher caste. Even those with access to improved toilets and piped water were also relying on open drainage, something that could compromise their health. Policies need to geographically and socioeconomically target the provision of adequate drains. Doing so is critical for removing disease-spreading contamination from the environment in order to prevent morbidity.

Methods

Data

The National Family Health Survey (NFHS-5) conducted between 2019 and 2021 was led by India’s Ministry of Health and Family Welfare, Government of India, and the International Institute for Population Sciences and is a part of the Demographic and Health Surveys program. These surveys employ rigorous methods and procedures to ensure the production of high-quality environmental health data that have been used to publish hundreds of peer-reviewed articles32,33. There have been four prior versions of the NFHS dating back to 1993. However, NFHS-5 is the first round to include data on the type of drainage available to a household.

Sampling strategy

The NFHS-5 sample contains data from 636,699 households, the unit of analysis for this study. These households were drawn from all of India’s 36 states and Union Territories. Additionally, the NFHS-5 sampled households from each of India’s districts and 30,170 Primary Sampling Units (PSUs), urban and rural communities within each district, which were selected based on their population size. NFHS-5 relied on the 2011 census for its sampling frame of Primary Sampling Units (PSUs)19. These PSUs are wards in urban areas and villages in rural communities, and were selected based on their population size. The list of PSUs for NFHS-5 was confirmed in 2017, and as of March 31st of that year, these PSUs were nested in 707 districts19. The 636,699 households were then randomly selected from PSUs. A complete description of this sampling strategy is outlined in the NFHS-5 report17.

Study population

This study analyzed all 636,699 households in the NFHS-5 dataset as there was no missing outcome data. Furthermore, the NFHS-5 dataset has complete data on household wealth, education of the household head, caste, and household location (urban versus rural). The percent of households in each category is shown in Table 1.

District geometry

NFHS-5 contains data from 707 districts as of March 31st, 2017. More have been added since as states in India are continuously updating their district borders and geographies for administrative purposes. But the data required to update these district boundaries is not always readily available. As such, this analysis does not cover the full set of current districts.

This analysis, however, examined household drainage types across 720 districts. Including 720 districts was possible by updating the district geometry for Andhra Pradesh (AP), a state in south India. The state created 13 new districts by modifying the existing 13 districts in April 202234. Updating the district geometries for AP is important because none of the district geometry from NFHS-5 in AP matches the updated district boundaries, which would prevent any conclusions to be drawn about the prevalence of drainage types in the districts of the state. Thus, to include the updated district geography from AP we used the Assembly Constituency (AC) to district linkage information provided by the Chief Electoral Officer (CEO) of Andhra Pradesh34. ACs are political areas within each state from which Members of Legislative Assembly (representatives in the state legislature) are elected, and each district throughout India is comprised of ACs. In the case of AP, ACs are contained within district boundaries (they do not overlap different districts). Therefore, because which ACs are in each new district is known, the AC shapefiles can be used to create the updated district boundaries for AP 34. NFHS-5 PSUs were then spatially joined to the new AP district shapefile to ascertain the new district linkages for each PSU in AP only. For other states, the PSU to district linkage that existed in the microdata were used.

Outcome

We included four drainage type outcomes in this study. These were based on the household surveyed administered by NFHS-5. These four drainage outcomes were: (a) no drainage, (b) open drainage, (c) drain to soak pit, and (d) closed drainage. We estimated the prevalence of each of these outcomes. There were no missing data for any of the four drainage types.

Statistical analysis

We estimated the weighted prevalence (and 95% confidence interval) of no drainage, open drainage, drain to soak pit, and closed drainage for all 720 districts. We also calculated the interquartile range (IQR) for the district prevalence of each outcome. In this case, these values indicate the gap between the first and third quartiles of the district prevalence of each outcome. We also examined the proportion of drainage type by improved and unimproved toilet. Improved toilets are those that are not shared between households in which excreta is safely disposed of in situ or removed offsite5. Unimproved toilets are those that are either shared between households, even if they hygienically remove excreta, or toilets that have a pit without a slab or platform, hanging latrines, or bucket latrines5. Furthermore, we examined the prevalence of drainage type by whether or not a household had access to piped water. We also examined the prevalence of each drainage type by household wealth quintile, highest education attained by the household head (no education, primary education, secondary education, and higher), and caste (no caste, do not know, Scheduled Caste, Scheduled Tribe, Other Backwards Caste, and other). A full description of the socioeconomic variables included is provided in Table 1.