In very poor countries, the family that has to walk miles to fetch drinking water from a well or a stream may be the lucky one. In many villages, the water source is a filthy pond trod by animals and people, or a mud puddle out next to the yam field.

As a result, about 6,000 people a day — most of them children — die from water-borne diseases. Vestergaard Frandsen, a Danish textile company that supplies water filters to the Carter Center guinea worm eradication program and mosquito-killing plastic tarps to refugee camps, has come up with a new invention meant to render dangerous water drinkable.

The invention is called Lifestraw, a plastic tube with seven filters: graduated meshes with holes as fine as 6 microns (a human hair is 50 to 100 microns), followed by resin impregnated with iodine and another of activated carbon. It can be worn around the neck and lasts a year.

Lifestraw isn’t perfect, but it filters out at least 99.99 percent of many parasites and bacteria, the demons in most fatal cases of diarrhea. It is less effective against viruses, which are much smaller and cause diseases like polio and hepatitis, and it wouldn’t protect American backpackers against the parasite giardia. Nor does it filter out metals like arsenic, and it has a slight iodine aftertaste (not necessarily a bad thing in the large stretches of the globe with iodine deficiency).

It can be manufactured for about $3, but it needs more field-testing. Only about 100,000 have been handed out, 70,000 to earthquake victims in Kashmir last year. Already in the works, however, is a Lifestraw toddler version — which will be squeezable.