He went to Kenya with a sachet of powder and came back with a different job

What the powder does

It is not complicated, which is the point. The sachet contains iron sulfate, which Allgood's colleagues used to describe as a dirt magnet. It grabs everything suspended in the water, including worms and parasites, and clumps it together until the clumps are heavy enough to sink. A disinfectant in the same packet kills what is left: cholera, dysentery, typhoid.

You stir, you filter it through cloth, you wait twenty minutes. Brown water becomes clear water.

Allgood has described the moment the water cleared and Mercy's face changed. He has also described what it did to him, which was less comfortable. He had known the numbers for years, roughly a thousand children a day dying from illnesses tied to water, sanitation and hygiene. Standing at the pond, the number stopped being a number.

God called me out of the pew.

The part where it nearly didn't happen

The product was called PUR, and P&G could not sell it.

It worked. It just did not make money, which inside a consumer goods company is the only argument that counts. Leadership were discussing shutting it down.

Allgood proposed something the company had not done in its entire history: run it as a not-for-profit programme instead. His boss said yes, then asked him to write down what success would look like in five years.

His first draft came back rejected for being too timid.

So he wrote a second one. In it, P&G's retired chief executive personally hands over the billionth litre of clean water. At the time the programme had produced about thirty million.

They passed a billion. The Children's Safe Drinking Water programme has now passed 26 billion litres.

His first draft came back rejected for being too timid.

On being asked to describe success five years out

What he did next

He retired from P&G in 2013 and went to World Vision, where he runs water and health.

He found out afterwards that the leadership there had prayed over a list of candidates before approaching him, and that his name was on the list. Make of that what you will; he clearly has.

In the last decade World Vision has reached more than 37 million people with clean water. The organisation's own figure is that it now reaches one new person every ten seconds. It has finished its work in Rwanda, and is close to the same point in Zambia.

The wider number is the one worth sitting with. Since 2000, 2.1 billion people have gained access to clean water. Fewer than 700 million are still without it. A problem that was once simply a fact about the world is now a problem with an end in sight.

The advice, which is better than most

Allgood is a man in his sixties writing about calling, which usually produces something you could embroider on a cushion. His is more practical than that.

Look for the place your skills and your passion overlap, he says, and expect whatever you find there to involve serving somebody else. Pray about it and watch for confirmation rather than waiting for certainty. And do not let a failure disqualify you, which from a man whose flagship product was nearly cancelled is not an abstraction.

Then the line he closes on, which is the whole thing in three words.

Find your pond.

Why it belongs here

This magazine is named after a parable about three people handed different amounts and judged on what they did with them. The one who buried his portion did it out of caution, and caution is what the story is hardest on.

Allgood's portion was a sachet of iron sulfate that his employer was about to discontinue. He appears to have been the only person in the building who thought it was worth something.