Like magic: A purifying powder can turn muddy water clear, and safe.

They took a bucket of muddy, bacteria-laden water. Added a bit of white powder. Stirred.

And within minutes, standing amid 100 refugees in war-torn Liberia, researchers from Johns Hopkins University had produced what seemed like a magic trick:

Clear, drinkable water.

"I couldn't believe it when I saw it," Hopkins researcher Shannon Doocy said of her work last year. "The people in Liberia couldn't believe it."

The powder, developed by Procter & Gamble Co. with the federal Centers for Disease Control and Prevention, is now headed for its biggest test yet: the tsunami zone.

Relief agencies, led by AmeriCares of Stamford, Conn., are sending over at least 15 million packets of the stuff - enough to purify 40 million gallons of water. Health officials yesterday said the lack of potable water represented a grave threat to survivors. Water and sewer plants have shut down, and pipes are ruptured, leading some victims to drink sewage water.

Relief workers have been treating water for decades with chlorine bleach, which kills most germs but does not improve the water's appearance.

The new powder, called PUR, contains chlorine but has other ingredients that give it two key advantages. PUR gets rid of toxic "heavy metals," such as arsenic and mercury, and it makes muddy water look clean - a key to winning acceptance from those who may be leery of aid from outsiders.

"People need to believe that they're drinking water that's purified," said Jeff Albert, an environmental scientist at Brown University who is helping raise money for AmeriCares.

The added ingredients - primarily iron sulfate and clay - cause particles in the water to clump together and settle to the bottom, so they can be strained out through cloth. The process, known as flocculation, is used in many municipal water-treatment plants, including Philadelphia's, but the powder has not previously been made in small packets for widespread public use.

PUR has other advantages. Unlike boiling water, it does not require energy on site. And it is much lighter and easier to transport than fresh water.

It costs Procter & Gamble about 8 cents to make each packet, or "sachet," of powder, said Gregory S. Allgood, director of safe drinking water for the Cincinnati-based corporation. The company has donated most of the sachets, which are about the size of a ketchup packet.

About one-third were sold for a nominal fee - 3.5 cents per packet - as a signal to relief workers that it has some value, to encourage that it be used correctly and responsibly, Allgood said.

For now, the supply is limited. The amount being shipped to Sri Lanka and other tsunami-ravaged nations represents the company's entire global inventory.

P&G formerly made the powder in the Philippines, through a contractor, and has switched to its own plant in Karachi, Pakistan, where it is ramping up production.

In addition to providing the product to nonprofit groups, the company tried in the past to sell the powder for profit. That effort had limited success, but P&G will continue to manufacture the product for humanitarian use, Allgood said.

The PUR brand also is used for the company's home water-treatment filters, which use a different technology involving carbon.

The powder packets, besides being used in emergencies, are gaining favor as a long-term solution in countries where clean water is unavailable. Population Services International, a Washington-based nonprofit, recently has used PUR in Uganda and Kenya, vice president Sally Cowal said.

Worldwide, the number-one goal for PUR and other treatments is to prevent diarrhea, which is believed to kill 5,000 children every day.

The product is not a panacea. It will not purify raw or undiluted sewage.

But the powder has proven its worth. Last year in Liberia, the Johns Hopkins researchers found that people using PUR were one-eighth as likely to contract diarrhea as those drinking untreated water. Children under 5 were one-twelfth as likely to get the disease if they drank treated water, said Doocy, who works at the university's Bloomberg School of Public Health.

As for the Indian Ocean disaster, P&G suffered its own loss. Its country manager in Thailand, Orapim Milindasuta, was killed in the tsunami.