It's something we've heard again and again from health authorities in the coronavirus pandemic. Wash your hands. Frequently. With soap and water. For at least 20 seconds. That's an effective way to eliminate viral particles on your hands.

But for the 2.2 billion people in the world who lack safe drinking water — mostly in low- and middle-income countries — that advice will be difficult to heed. In these places, water is scarce for a number of reasons. It could be due to drought or climate change. Or local water supplies could be contaminated. Or the nearest source of water may be far away from home.

Aid groups and public health officials are doing all they can to help people in these communities overcome the obstacles and wash up. Washing your hands, they say, is a small action that can make a huge difference in the coronavirus pandemic.

"Hand-washing is one important tool to check and control spread," says Amanda Glassman, executive vice president at the think tank Center for Global Development — along with other known interventions such as testing, isolating the sick and social distancing.

Water that is safe enough to drink is the best option for hand-washing. The ideal is to use clean, running water to wash away germs because it is less likely to contain harmful pathogens like e-coli, which can make you sick.

So how do you get water to those in need? Aid groups can truck in vast amounts of water, for example, but many say that's expensive and unsustainable.

In less than ideal circumstances, other types of water can be used to wash hands. Non-potable water (for example, water that's been used to clean dishes or do laundry) — along with soap — can be effective, according to a 2019 study published in the journal Environmental Science and Technology.

Small-scale solutions work, too – like setting up a network of public hand-washing stations – something done in West Africa during the Ebola outbreak of 2014. "When Ebola hit, one of the big concerns was the lack of running water and sanitation for hand-washing and proper waste disposal," says Joia Mukherjee, chief medical officer of Partners In Health and associate professor of global health at Harvard Medical School. "It almost seemed like an unsolvable problem. And yet relatively rapidly, solutions were put together."

The simplest kind of hand-washing station needs just two buckets. One bucket contained a mix of chlorine and water for the washing, with a spigot so people could tap into the supply, she explains. A second bucket, underneath the spigot, caught the wastewater.

These hand-washing stations were put in public buildings, schools and markets in Ebola-affected areas — and public health officials stressed why it was important to wash hands. Soon "people adopted this hand-washing technique everywhere," says Mukherjee.

Mukherjee was heartened to see these stations again in February on trips to Liberia and Sierra Leone — set up by the countries' health authorities to combat the spread of coronavirus. "I was very pleasantly surprised that they had already re-initiated this type of hand-washing at airports and outside of public buildings like the Ministry of Health. The lessons learned from Ebola were immediately being used."

This kind of innovation is exactly what the developing world needs right now to ward off coronavirus, says Glassman, who is the author of Millions Saved: New Cases of Proven Success in Global Health. "We should deploy and test everything we've got," she says, citing the hand-washing stations. "Affordability and fast availability is what matters now."

The lower the technology, the better, says Glassman. If people can use objects and materials available in their own communities, like buckets, it makes the solution more likely to work.

One such device — which has been praised by global water researchers — is the SE200 Community Chlorine Maker. Developed by the global organization PATH, it can make chlorine from just water, salt and a car battery. Chlorine is commonly used to disinfect water because it kills many bacteria and viruses but isn't always easy to obtain. The clean water can then be used to safely wash hands.

In preparation for the surge in coronavirus cases, 13 countries from sub-Saharan Africa as well as from Myanmar and Vietnam have put in requests to PATH for the devices. The group is finalizing logistics to get them up and running.

Then there's the question of how to keep hand-washing stations safe from being a hot spot for disease transmission. Myriam Sidibe, a senior fellow at the Harvard Kennedy School, is working with the aid group WaterAid in Kenya to figure that out. They are trying to find ways to make 10,000 water stations across the country safe for people to congregate around.

The plan is introduce "social distancing nudges on the ground, similar to what we are seeing in supermarkets in some countries," says Sidibe, who is based in Nairobi. "These can be red dots painted on concrete or if the surface is more uneven you can get stones or pieces of wood and sort of partially bury it in the dirt and then paint the visible bit red."

As for soap, it's not as much of a problem as water.

Soap is available to purchase almost everywhere in the world, says Sidibe. Most people, including those living in poverty in rural and urban areas, have some kind of basic soap, even if just for laundry, she says.

But in this time of crisis, soap supplies may run short — or people who lose their income because of the pandemic may find soap is not affordable.

In New Delhi, Sudhanshu S. Singh, CEO of the nonprofit Humanitarian Aid International, has been collecting donations of soap and hand sanitizer — increasingly in short supply as the city is in lockdown — for the 1,000 refugee families he serves in Delhi.

The families fled Pakistan from persecution and are living in camp settlements in a slum. Because they are stateless, they don't have the same rights to water as Indians living in the slum, says Singh, and have even less access to water. "They're living in absolute abysmal conditions. They're vulnerable to different kinds of diseases and health issues. Eventually the virus is going to affect them."

So far, he's distributed a 15-day ration of hygiene materials and taught them proper hand-washing. To ensure the families have enough water to wash their hands, he and other groups petitioned the government to bring more water to the part of the slum where the refugees live. Last week, the authorities brought in a tanker of water to provide additional supply for drinking and hand-washing and will do so regularly.

But offering soap and water is no guarantee that people are going to wash their hands. In every country, from high income to low income, there are a lot of folks for whom a thorough scrub is not a regular habit.

"Just instructing people to wash their hands is not going to get them to do it," says Sidibe, who previously worked at a project at Unilever focused on changing hand-washing behaviors in 55 countries. "People don't practice hand-washing. It's inconvenient and they have other priorities. To change behavior, you need to create an enabling environment. You need to establish a positive social norm. And you need to make it a desirable thing to do."

In Nigeria, where there are only 111 reported coronavirus cases so far, aid groups like UNICEF have been emphasizing the importance of hand-washing in the low-income areas they serve. "We are trying to spread the message through celebrities, community and religious leaders, and reaching out to media and radio stations," says Zaid Jurji, head of UNICEF's water, sanitation and hygiene program, based in Abuja.

They're collaborating with artists to sing about hand-washing, too.

On Sunday, UNICEF posted "We go win (Corona)" to their YouTube channel. It's an original song from the popular Nigerian musician Cobhams Asuquo.

The lyrics go, "Corona no big pass us ... as long as we remember to always do the right thing: wash your hands, love each other, we go win."

The idea that a song could change behavior may seem naive, but it did work during the Ebola outbreak.

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