All the panelists agreed with Ellsworth Havens — chairman of Rotary International’s program to find solutions to water and sanitation problems around the planet — that ensuring the fair distribution of potable water is “the greatest environmental issue confronting the world today.”

What provoked the most debate at the Katharine Cornell Theatre in Vineyard Haven on Saturday afternoon was the suggestion by another panelist, James G. Workman (author of Heart of Dryness), that the best way to guarantee that everyone gets the drinkable water they need might be through a system of privatization and trade of the supply.

Forty people attended the panel on worldwide water issues sponsored by National Geographic during the Water Is Life weekend. It was a day of summery sunshine and warmth as well as of bitter contemporary irony: One of the panelists, Alexandra Cousteau, did not attend because her advocacy group, Blue Legacy, was offering counsel to those dealing with the calamitous oil rig disaster spilling its effluent out across the Gulf of Mexico.

The program on Saturday afternoon was sailing along concordantly, with all five panelists agreeing with moderator William Waterway of Katama that mankind now understands that “changing our relationship with water is our next big step in our evolution.” The theme of the discussion was how people can fix environmental problems, such as water shortages, in the wider world by improving things close to home and spreading the news of success from there.

For instance, Lynne Cherry, a writer and illustrator of children’s books as well as a filmmaker, described a group of kids in Santa Monica who cajoled the city to ban plastic bags — a cause that cities are embracing elsewhere. Irena Salina, director of the acclaimed documentary Flow, described the purpose behind Written in Water, a new book published by National Geographic: 25 writers each personalize their relationship to water, describe the global crisis in graphic terms and offer ideas about how to save and protect fresh water for everyone.

It was Mr. Workman, author of Heart of Dryness, who suggested a possible systemized approach. His book recounts how the bushmen of the Kalahari responded to a demand by the government of Botswana to leave the desert for a reservation after the Kalahari began to draw the interest of diamond miners, cattlemen and even tourists. To move the bushmen along, the government began withholding the delivery of water to the tribes. But many of the bushmen remained, and drawing on 30,000 years of experience in an arid land, figured out how to gather and trade water, diversifying its use while at the same time making sure that nobody in the community died of thirst.

Over time, the government fell but the bushmen thrived.

The response to this crisis challenged Mr. Workman’s notions about the power and potential virtue of the profit motive. The bushmen, like humans everywhere, were acquisitive, behaving “exactly like us,” he said. “They are selfish, lustful, greedy, happy, laughing — all these wonderful things and all these negative things that are human.

“But what makes them extraordinary is that they found ways to adapt that I think we can learn from. Instead of fighting over water, water is the one thing that brings them together.”

Paraphrasing the environmentalist Aldo Leopold, Mr. Workman said that one of the spiritual dangers of not owning a farm is “thinking that your food comes from a refrigerator.” In the same way, “one of the of the spiritual dangers of not owning water [is that] we all assume water comes from the tap — that this is something that comes from a utility, that this is something we take for granted.” He added, “Government says water must be cheap, abundant and clean. But sometimes it can’t be all of these things without paying a price.”

He outlined a model whereby everyone is allotted 100 gallons a day for free. Using the Internet and a cap and trade system, those who use more pay a stiff price; those who use less can sell their surplus to a desirous neighbor, donate it charity, give it to the fire department, or return it to its source. “But instead of being punished for conservation,” Mr. Workman said, “you’re rewarded for conservation. You’re given an incentive to do all the wonderful things that we should be doing just as a matter of course.” At the same time, he added, users learn where water comes from, what its value is and where it goes.

This idea met with skepticism from fellow panelists and the audience. From the floor came a question about the danger of greed — unregulated and unstoppable covetousness — and Mr. Havens, of Rotary International, suggested that the water problem was too pervasive, fundamental and desperate to solve through mere incentivization: Only one per cent of all the water on earth is potable, he said, and the average woman in Africa spends eight hours a day just looking for enough of it just to keep her family alive. Water, he said, “should be a basic human right.”

Both Ms. Cherry and Ms. Salina declared that as soon as greed enters the picture, there is the risk that transnational corporations will use their money and influence to skew and corrupt a system like the one Mr. Workman described. Ms. Salina likened the danger to the influence of the corn industry, which she said takes over production of an essential food and gets away with using pesticides that cause cancer and pollute rivers to meet the mass demand it has created. “Can’t we go back somehow to more local?” she asked. Must residents on Martha’s Vineyard eat corporately produced food if it is possible to learn to eat seasonally off the land again? “I want to be really careful,” she said, “because talking about greed — there’s a lot of greed in those companies.”

Adam Geiger of Aquinnah — an underwater videographer for National Geographic and a principal in SeaLight Pictures, whose film Return to Shark Eden premiered Saturday night at the Capawock theatre in Vineyard Haven — agreed. He drew an analogy to smoking, saying that those who smoke raise the cost of health care for everyone who doesn’t, and he asked how anyone can have the right to pollute, waste, or overuse water when the rest of the world is so desperately needy. “How can we have water, in this country, that’s being purchased and sold when it belongs — should belong, pretty much — to everyone?” he asked.

Mr. Workman’s answer: “The downside to a human right to water that’s just given out and you can’t do anything with it — it’s just sort of yours for protection — [is that] then I think we have an incentive to waste that. Greed by itself is bad without the institutions, when it can’t be harnessed in a productive way.”