Scientists in America have designed a drinkable book that can save lives by making polluted water safe to consume.
It's an instruction manual with information on how and why water should be filtered.
Once read, its pages can be torn out and used to turn dirty water into drinkable water.
The "drinkable book" combines treated paper with printed information on how and why water should be filtered.
Its pages contain nanoparticles of silver or copper, which kill bacteria in the water as it passes through.
In trials at 25 contaminated water sources in South Africa, Ghana and Bangladesh, the paper successfully removed more than 99% of bacteria.
The resulting levels of contamination are similar to US tap water, the researchers say. Tiny amounts of silver or copper also leached into the water, but these were well below safety limits.
The results were presented at the 250th national meeting of the American Chemical Society in Boston, US.
Dr Teri Dankovich, a postdoctoral researcher at Carnegie Mellon University in Pittsburgh, developed and tested the technology for the book over several years, working at McGill University in Canada and then at the University of Virginia.
"It's directed towards communities in developing countries," Dr Dankovich said, noting that 663 million people around the world do not have access to clean drinking water.
"All you need to do is tear out a paper, put it in a simple filter holder and pour water into it from rivers, streams, wells etc and out comes clean water - and dead bacteria as well," she told BBC news.
The bugs absorb silver or copper ions - depending on the nanoparticles used - as they percolate through the page.
"Ions come off the surface of the nanoparticles, and those are absorbed by the microbes," Dr Dankovich explained.
According to her tests, one page can clean up to 100 litres of water. A book could filter one person's water supply for four years.
Instructions are printed on the book's pages, in English as well as the local language
Dr Dankovich had already tested the paper in the lab using artificially contaminated water. Success there led to the field trials which she conducted over the past two years, working with the charities Water is Life and iDE.
In these trials, the bacteria count in the water samples plummeted by well over 99% on average - and in most samples, it dropped to zero.
"Greater than 90% of the samples had basically no viable bacteria in them, after we filtered the water through the paper," Dr Dankovich said.
"It's really exciting to see that not only can this paper work in lab models, but it also has shown success with real water sources that people are using."
One location gave the paper a particularly tough challenge.
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