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Delhi's Sewage Spillovers

Blog Post2 min read

We have already talked in depth on this blog about how open defecation is worse for health in more populated areas. Because the fecal germs of one person can make anyone sick, the health effects related to open defecation are worse in areas where the likelihood of being exposed to other people’s fecal germs is higher. As the number of open defecators increases in a given area, the health effects will be more pronounced. In fact, children growing up in areas with a greater incidence of open defecation per square kilometer are on average shorter.

Our friend Jeff Hammer and some of his colleagues have spent the summer delving into this issue further by exploring how health outcomes may be geographically distributed over very population-dense areas, the slums of Delhi. I recently saw Jeff present some of the preliminary results from this research here in Delhi at NCAER.

They mapped out open defecation areas, open sewers, sewage outflow areas, and garbage dumps, all places where one could come into contact with fecal pathogens, and interviewed households around these areas. Their initial hypothesis was that individuals who lived closer to unsanitary places were more likely to have diarrhea, but what they ended up realizing was that there are lots of minute, hard-to-measure characteristics that mediate exposure to fecal pathogens from the surrounding environment. For instance, whether the gradient of the pathway outside is tilted toward or away from the house, or whether a hut is slightly lower lying or slightly raised are the kinds of factors that determine whether and how often fecal pathogens enter the home. But there are too many of these little micro-level details that are important. It would be almost impossible, or at least very expensive, to collect data on all of them. So the researchers cleverly decided to use a variable that gets at what really matters: whether water from the street has come into the house in the last year.

What they find is that individuals who reported having diarrhea in the past two weeks are significantly more likely to live in houses that have had water from the street enter the home in the past year. Incidence of diarrhea in the past two weeks also increases with the number of open defecators within 2.5 kilometers (using GIS data) and with someone in the household sometimes defecating in the open. These results are robust to the inclusion of controls like education, gender, water source, caste, neighborhood, and age. And the results do not hold for other types of health conditions like fever and cough, which suggests that its not that these people are just unhealthy.

One thing that I like about this study is that it reminds us again of the importance of sanitation spillovers. Using household-level data and a more proximate measure of health (incidence of diarrhea), this study arrives at the same conclusions as studies that use more aggregated data from the Demographic and Health Surveys and a more long-term measure of child health, height (see here and here). All of these studies come to the same conclusions: there are externalities associated with sanitation.

Importantly, it also highlights the point that where stuff flows afterwards is as important as where stuff goes in the first place. Not only is it important to get people to use latrines and toilets, it is just as important to make sure that what goes into the toilet does not just find its way right back into peoples homes afterwards.

You can see Jeff’s slides from his presentation at NCAER here.


r.i.c.e. is a non-profit research organization focused on health and well-being in India. Our core focus is on children in rural north India. Our research studies health care at the start of life, sanitation, air pollution, maternal health, social inequality, and other dimensions of population-level social wellbeing.

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