Writing in this magazine seven years ago, the Princeton ethicist Peter Singer argued that affluent Americans have a duty to donate a substantial portion of their wealth to the developing world. Taking inspiration from the multibillion-dollar stock grants made by Bill Gates and Warren Buffett to the Bill & Melinda Gates Foundation, Singer proposed a sliding scale that called for the wealthiest families to give away a third of their annual income. Anyone in the top 10 percent, he recommended, should at least tithe. “In the real world,” Singer wrote, “it should be seen as a serious moral failure when those with ample income do not do their fair share toward relieving global poverty.”

As ethics, the argument is difficult to assail, but as a sales pitch it’s a little flat. Rates of charitable giving have fallen since 2005. Last year, Americans gave 2 percent of their income to charity, slightly less than they gave in 1971, according to an annual survey conducted by Giving USA. And it’s here that Harrison — and his many acolytes in Silicon Valley — think they can change things. “Charity: water is a very different kind of nonprofit, and it has everything to do with Scott,” says Andy Smith, a marketing consultant and co-author (with his wife, Jennifer Aaker, a Stanford professor) of “The Dragonfly Effect,” a book that focuses on nonprofits. The world of charitable giving, Smith says, has traditionally attracted people with an aversion to business. “Now you’re having people with more of a business mind coming into the sector,” he says. “These are people who are good at persuasion, at making something cool.”

When Harrison founded charity: water in New York City in 2006, he initially intended to counter the cynicism of his club buddies. “I wanted to create a model that would put all the excuses aside,” Harrison says — a charity, in other words, for people who didn’t trust charities. To pre-empt objections to high overhead and waste, Harrison set up two bank accounts: one, raised chiefly from a handful of wealthy individuals, to pay for administration and fund-raising; and the other to finance the digging of wells and other water-related projects in the developing world. Today the organization’s heavily promoted “100% Model” allows it to claim that every dollar donated to water is actually used that way. (Some consider this more a matter of marketing than anything else, but even so, charity: water is a relatively efficient organization, earning a nearly perfect rating from Charity Navigator, a sort of Consumer Reports for the nonprofit world.) Many donations are earmarked to specific projects, so if a church group gives, say, $5,000 for a well in Ethiopia, its members are not only told where their $5,000 is spent, but they also receive pictures of the well they financed and its G.P.S. coordinates. All of this information is publicly available on a section of charity: water’s Web site dedicated to “proving it.” Most donors who happen to visit their well will find their names on a plaque there.

In just seven years, Harrison’s organization claims to have raised roughly $100 million — $33 million in 2012 alone, up from $27 million the year before and $16 million the year before that. Today it is the largest nonprofit in the United States focused on water, with revenues that are four times as great as those of Water.org, the group co-founded by Matt Damon. Charity: water doesn’t drill wells or buy water filters but acts as a fund-raising clearinghouse for locally based charities, which it subcontracts to do the actual work. It markets its partners, mostly using its Web site and social media. “You could almost imagine us a Kayak.com or an Expedia,” Harrison says. But charity: water promises to do more than a mere online travel agent does; it claims to verify that the wells its donors buy are actually completed in a timely fashion. “We create an experience,” he says, “a pure way to give.”

Harrison’s commitment to geeky transparency, his willingness to speak the language of Silicon Valley and especially his organization’s impressive revenue growth have made him a hero to techies and to a growing class of tech-savvy philanthropists. “Scott is one of a handful of social entrepreneurs who are disrupting philanthropy,” says Laura Arrillaga-Andreessen, the founder of the Stanford Center on Philanthropy and Civil Society (and the wife of Netscape’s founder, Marc Andreessen). She’s also an enthusiastic charity: water supporter. The organization, she says, “is making philanthropy sexy.”

Ours was the only plane at Alula Aba Nega Airport in Mekele — a small, dusty city 500 miles north of the Ethiopian capital, Addis Ababa — when we landed the following afternoon. After customs officials flown in from the capital finished looking over our entry documents, we boarded a convoy of white Toyota Land Cruisers, with the numbers 1 through 20 taped to the sides, and made our way into the mountains.