This spring the World Health Organization (WHO) celebrated the early completion the 2015 development goal of bringing improved drinking water to an additional two billion people since 1990.

"Today we recognize a great achievement for the people of the world," United Nations Secretary General Ban Ki-moon said at the occasion. "The successful efforts to provide greater access to drinking water."

The feat was a landmark in securing what the U.N. General Assembly declared in 2010 was a universal human right: "access to safe and clean water." In an effort to improve health and quality of life across the world between 1990 and 2015, the U.N. established eight Millennium Development Goals (MDG). One of the sub targets was to "halve, by 2015, the proportion of the population without access to safe drinking water and basic sanitation."

And by early 2012 only approximately 800 million people around the globe still relied on "unimproved" water sources such as streams, ditches or unprotected wells, which are the most likely places for contaminated water. Pipes, boreholes and protected wells are much more likely to prevent contact with dangerous pathogens, chemicals or sewage runoff.

But just because water is pouring out of a spigot does not mean that it is safe to drink. In poorer areas, where infrastructure and sanitation are often much worse, even sources of water that have been "improved" are frequently at risk for contamination by human and animal feces, according to recent analyses.

Improved but not necessarily safe

One report, published earlier this year in the Bulletin of the World Health Organization, analyzed water quality test data from five countries (Ethiopia, Jordan, Nicaragua, Nigeria and Tajikistan) and found that many sources of "improved" water failed the safety test. When these improved waters were tested and compared with survey data about where people got most of their water, the estimates for the populations that have access to safe drinking water fell by 16 percent in Nicaragua, 15 percent in Nigeria, 11 percent in Ethiopia and 7 percent in Tajikistan. (Jordan, which primarily uses public utilities to pipe water, remained at a relatively high percentage.) Additionally, the study authors noted, the number of people who had access to safe—and not just improved—water in 1990 was likely much lower than previously estimated, which means that the 2015 target is even farther away than estimated by the current rubric.

Extrapolating from these five very different countries spread over three continents to the rest of the globe is difficult. But one group of researchers at the Gillings School of Global Public Health's Water Institute at the University of North Carolina at Chapel Hill took a shot at it in their March International Journal of Environmental Research and Public Health paper. They estimate that some 1.8 billion people—28 percent of the population worldwide—was using unsafe water as of 2010. That is far more than the 783 million (or 11 percent) estimated by WHO and UNICEF to have access to improved water sources. The researchers acknowledge that their "estimate is imprecise," but "the magnitude of the estimate and the health and development implications suggest that greater attention is needed to better understand and manage drinking water safety." And other experts in the field agree that their estimate is a good ballpark figure for the true disparity.

This disjunction could have large implications for public health planning. In many water-insecure places, diarrheal disease is still a leading cause of death—especially for children, of whom some 1.5 million succumb to these infections. Most of those illnesses result from contact with bacteria, viruses or parasites, often through unclean water. A recent study in Environmental Health showed that access to clean water could reduce childhood mortality by 1.17 deaths per 1,000 children, which is a large number of preventable deaths for the millions of children who lack access to improved water—and millions more who apparently lack access to fully safe water supplies.

These preventable diseases also cost countries dearly in lost productivity. Poor sanitation can demand high environmental cleanup costs, and are a major drag on economic growth, notes Jaehyang So, manager of the Water and Sanitation Program at the World Bank.

Global challenge

Gathering data about the type of water source—tap, drainage ditch, borehole, etcetera—is a lot easier than performing formal water quality tests, which is one of the reasons the U.N. goals focused on improving water sources.

"The problem is that there is not really any good, objective water quality test" that can easily be performed in remote areas of developing countries, says Stephen Gundry, professor of environmental engineering at the University of Bristol who co-authored the WHO Bulletin paper.

The U.N. is not blind to this disparity. Many experts at the organization "have let Mr. Ban know in no uncertain terms that his office has badly understated the scale of the drinking water crisis," environmental analyst Roger Harrabin wrote earlier this month in his column for BBC News.

"These targets are set in a very political environment," says Sanjay Wijesekera, chief of the U.N. Children's Fund's (UNICEF) Water, Sanitation and Hygiene Programme division. And once the goals are established, he and others working on the challenges are tasked to try to help as many countries as possible meet them.

One of the biggest breakdowns between improved and safe water occurs almost imperceptibly over time. Creating an improved water source does vastly increase the odds that water will be safe. But if pipes, wells and other improvements are not maintained over time, they can become damaged or compromised, allowing bacterial contamination in.

With the focus on installing pipes, wells and other improvements, localities and organizations have not always kept up the gains they have made. Wijesekera points out that UNICEF programs, such as those in eastern and southern Africa, emphasize sustainable water improvements. These initiatives have an annual sustainability check to make sure facilities have both technical and financial support to keep them running safely. But as Gundry notes, continued maintenance often does not garner extra credit or funds, allowing once-safe installations to fall into disrepair.

All of these new pipes and wells "have been very effective in bumping up the numbers" for the MDGs, Gundry says. But the bottom line is that U.N. officials "focused on an indicator that doesn't tell the whole story," he notes. "They just accepted that an improved source is a safe source, which it isn't, of course.”

Additionally, many people still have to transport water from a source back to their homes—a period when contamination can occur. Contamination is likely "somewhere along the way," Wijesekera says, from unsanitary containers or handling. The World Bank's So notes that some 40 percent of home water samples studied in India that were clean upon collection had been contaminated by the time they were ready for consumption at the home. But measuring those levels on a broad scale would mean testing water in homes, which is even more difficult than the area testing.

Wijesekera notes that there are numerous pilot programs around the globe that are testing in-home treatment technologies. But these can also be a burden on those who use them, so the hope would be to eventually have water piped much closer to home—if not in the actual premises.

Portable potable test

One of the reasons that the U.N. relies on improved sources as a measure of drinking water access rather than actual safety is that the latter is much more difficult to assess than counting wells and spigots. "It just isn't feasible to do bacterial tests," Wijesekera says.

"Over the last 20 years, there has not really been the capability in most developing countries to test water across the country," Gundry notes. For traditional, standard tests, water samples need to be kept below 4 degrees Celsius after collection until they are delivered to a lab where they can be cultured and examined under a microscope for microorganisms, such as Escherichia coli. To maintain that cool temperature, technicians need ice, which is often unobtainable in remote villages that do not have electricity. And labs are often ill-equipped and far away. "The barriers to getting samples in developing countries are fairly insurmountable," Gundry says.

Many groups are trying to tackle this problem. The challenge, Wijesekera says, is to make a test that is affordable, quick and can be used easily by people in the field who are not water quality experts.

Gundry and his colleagues have developed one possible solution. Called Aquatest, it is a compact, field-ready tool that provides a simple reading about the presence of E. coli within about 24 hours. They now have some 20,000 devices out in the field being used globally, and they are looking for a commercial partner to help increase production and distribution. But this and other devices will likely need much more evaluation before the U.N. and others can confidently mandate this sort of on-site water safety testing worldwide to truly get a bead on global access to safe water.

New focus on safety

Those at the U.N., WHO, UNICEF and other organizations are already starting to discuss how assessments might change after the 2015 MDG deadline has passed and the international community sets new targets. Gundry and others are hopeful that water safety will garner higher priority.

In the absence of better water safety data, Wijesekera notes that improved measurement of water sources is at least the best indicator that they currently have. And it underscores the progress that has been made in delivering protected water supplies to more people.

Nevertheless, whether there are 800 million or 1.8 billion people who lack safe water, the scourge of preventable deadly diarrheal and other waterborne diseases will continue to plague too many.

As Wijesekera points out, even the current WHO statistics "draw attention to the unfinished agenda" of improved water reaching another 800 million people and safe water reaching some one billion more. "It's not just enough to make progress on a broad front," he says. But many of these people are among the poorest 20 percent on the planet and can be "the hardest to reach—physically and politically," he notes.

And those who are falling into the gap, who have improved but unsafe water, are likely going to be difficult to help as well, especially without widespread, affordable water quality tests. Moving people from surface water collection to a new, protected well is much easier to see as progress than repairing a old well's housing. As the development community continues to focus on installing new pipes and drilling new wells for the large number of people with unimproved water sources, those whose infrastructures had been improved but are now failing often fail to get as much aid and attention.

To So and her colleagues at the World Bank, water safety is inseparable from sanitation—access to which lags far behind clean water. The need for clean water is apparent to almost everyone, she notes, but in many areas where open defecation is still the norm, the demand for sanitation is just not there yet. And where proper sanitation is scarce, any vulnerable water sources are much more likely to become contaminated.

By the U.N.'s development goals, sanitation is not expected to meet the target improvements by 2015. By the World Bank's count, poor sanitation—and its subsequent contamination of water supplies—costs India some $53.8 billion each year (some 6.4 percent of the country's entire gross domestic product), not to mention untold number of deaths and illnesses. And as a threat to safe drinking water, So says, "sanitation is the big crisis." Further, simply plodding toward its 2015 target is keeping millions in jeopardy of unsafe water. "Improvements cannot be 'slowly but surely,'" So says. "It's taken way too long for the world to get rid of a simple problem."