When you turn on your tap, how confident are you that water will flow out? If the answer is “very”—no matter the time of day—then you are enjoying one of the benefits of a continuous water supply.

Having water piped into your home is considered a luxury in many parts of the world. But even if a water pipe does connect to a house, it may only transport water on a part-time basis. This is called intermittent water supply.

Intermittent water supply is more than an inconvenience: it can be hazardous to human health. Epidemiologists and engineers from UC Berkeley recently teamed up to learn how health was impacted by how often a home receives running water. The researchers followed nearly 4,000 households in Hubli-Dharwad, India over a 15-month period to track health effects stemming from intermittent water supply.

“There’s reason to believe that intermittent supplies … would be associated with increased burden of waterborne disease,” says Ayse Ercumen, an epidemiologist at the UC Berkeley School of Public Health and lead author on this study. With intermittent water supply, old or worn-down water pipes can accumulate small cracks or breaks. When these breached pipes come in contact with animal feces, human feces, or sewer pipes, contamination can be sucked into the pipes because of the low or negative pressure. This so-called “intrusion” is greatly reduced if continuous water pressure is allowed to keep the dirty water out.

The researchers chose to study Hubli-Dharwad because a portion of the community was recently upgraded from intermittent to continuous water supply. “[It] gave us a really great opportunity to do an impact evaluation,” says Ercumen.

Because only a portion of the community upgraded to continuous water, researchers could isolate whether water supply independently improved human health—and what they found surprised them.

“This is the most well designed study to date regarding intermittent water supply and diarrheal disease,” says Aaron Bivins, a graduate student at the Georgia Institute of Technology who also studies intermittent water supply and was unaffiliated with this study. Previous studies on the subject were strictly observational, which can introduce bias that might affect the results. The Hubli-Dharwad study features both an intervention group (those who were upgraded to continuous water supply) and a control group (those who were not). “Including a control [group] allows us to draw firmer conclusions about the relationship between intermittent water supply and diarrheal disease compared to purely observational studies,” says Bivins. “Those of us interested in [intermittent water supply] have learned a lot from this study.”

Residents of Hubli-Dharwad fill storage containers to ensure they have continuous access to water in the face of an intermittent supply water system. Because water pressure in the pipes is often so low, the faucet is located below ground level, and frequently floods during the rainy season. Credit: Kara Nelson

The water flowing for the first 20-30 minutes after an intermittent water supply system is turned back on is often too contaminated to drink. After about 30 minutes, however, most of the dirty water has moved out of the system, found Kara Nelson, a professor in UC Berkeley’s Department of Civil and Environmental Engineering and a collaborator on Ercumen’s study. “We recommend that the first water that comes out of the pipes is not used for drinking,” says Nelson. She added that knowledge about this flushing phenomenon could inform people on how to best cope with the health risks of intermittent systems.

In households where water is an uncertain commodity, people will often fill up large containers whenever the water comes on. These containers then sit inside or near the house, where they come into contact with dirty hands, curious children, or pots and pans that have been sitting on the ground. As a result, the water can become even more contaminated.

It is clear that some health risks are associated with intermittent water supply. However, the researchers in Hubli-Dharwad uncovered unexpected results: there was no significant difference in diarrheal disease when the two populations were directly compared.

In other words, the people using the upgraded, continuous water system did not experience significant health benefits. “In this particular setting, people unfortunately continued to store drinking water, even though they had a [continuous] drinking water supply in their home,” says Ercumen. “I think that was mostly habit driven.” She said that the continued storage of this water likely resulted in recontamination and potentially lessened the health benefits of a continuous water supply.

“The findings were mixed, but that’s not surprising,” says Bivins, the Georgia Tech researcher. One outcome that the study examined was self-reported diarrhea. The bacteria that make people sick with diarrhea can be passed along by a number of different transmission routes. Although some of these do go through drinking water, others do not, Bivins explains, supporting Ercumen’s ideas that the contamination could be coming from a source besides the continuous supply system.

Considering the bigger picture, a huge problem is simply the lack of awareness of the dangers caused by improper use and management of water systems. “Most people don’t even know this is a problem, this issue of continuous versus intermittent water supply,” says Nelson. “Many of the decision-makers have what I like to call ‘virtual water supply.’” Middle- and upper-income residents in areas that regularly experience water outages can circumvent these problems by installing a large roof tank with an automated pump that fills with water when the main system is on. Some of these people are the ones passing policies and making decisions about the rest of their communities, even though they may not perceive a problem.

“Something like intermittent piped water is probably a million times better than drinking from a pond,” Ercumen says. “But it doesn’t necessarily stop there … [The piped water systems] also need to be upgraded in a way that protects public health further.” Ercumen adds that it is important to remember that just because a water system is implemented, the change does not guarantee health benefits. “Is it sufficient to just intervene on the water routes, or do you also need to do other things to have a discernible impact? It seems like in this particular setting, just impacting the waterborne route did not necessarily translate specifically into health impacts.”