Throughout the Oakland hills, other volunteers are taking water samples from the creeks that feed into the lake, including Wildwood Creek, Pleasant Valley Creek, Bushy Dell Creek, Trestle Glen Creek, Indian Gulch, Broadway Branch, Glen Echo Creek, Cemetery Creek, and Rockridge Branch.

The volunteers are all members of the UC Berkeley chapter of Engineers for a Sustainable World, known as ESW-B for short. Nguyen, a senior at Cal, is project manager of ESW-B's Lake Merritt Project.

"We're trying to pinpoint where the nitrogen pollution in the lake is coming from," he says. "A few years ago, the EPA declared Lake Merritt an 'impaired body of water' because of the low oxygen levels, and everybody started studying oxygen levels. But we think that may be a symptom of a larger problem: nitrogen pollution from urban runoff, which has hardly been studied at all. We aim to correct that."

Two people jogging around the lake stop and ask Nguyen what he's doing. When he tells them, they break into smiles and say, "Hey, that's great! Thank you!"

"I know how they feel," he says later. "I've jogged around this lake so many times myself. Knowing that this project will safeguard the lake for the enjoyment of future visitors and inhabitation of wildlife makes getting up in the morning easy."

That same day, Ashley Murray is at The Potter's Studio in Berkeley, dropping off the latest batch of ceramic disks for firing. Murray, a second-year grad student, is project manager of another ESW-B project: developing low-cost water filters for people to use in a slum in Bombay, India, called Bheram.

"They're getting sick from sewage-contaminated drinking water," she says. "We're trying to design a filter that's long-lasting, easy to maintain, constructed from local materials and -- above all -- cheap. If it costs more than $5, nobody will be able to afford one."

There are water purification devices already on the market, but Murray thinks they're not good enough.

"Their flow rates are too slow," she says. "The people in Bheram have running water for only two hours a day for all their needs for the whole day, including washing and bathing. If the flow rate is less than four liters an hour, they won't have enough."

She and her team are experimenting with several prototypes, each with a different mixture of clay and combustible material.

"The combustibles burn off when we fire the disks in the kiln, leaving a porous ceramic," she says. "What we're looking for is the perfect mixture. If the ceramic isn't porous enough, the water won't flow easily. But if it's too porous, the filtration won't work."

After firing, the prototypes are dipped in a silver nitrate solution, dried, then soaked in salt water. The salt binds with the nitrate and precipitates out, leaving a microscopic coating of pure silver, which is the actual germ-killer.

The final selection won't be made until next month, when Murray and her suitcase full of prototypes fly to Bombay, where she'll confer with her colleagues at a local Indian NGO (non-government organization), the Committee for Right Housing. Next summer, production of the filters will begin in Bheram.

"We have three goals," she says. "Eliminate contamination in the drinking water, empower the community by reducing their dependence on government intervention to improve the water supply, and create an economic opportunity for the local craftsmen who will produce the filters."

In addition to the Lake Merritt and Bheram projects, a third ESW-B project will be launched this spring: installing solar desalinization units in 12 remote fishing villages in the Baja California peninsula. In the past two years ESW-B has also sent student interns to work on projects in Mexico, China Chile, Haiti and Guatemala.

The national organization was founded in 2002, and the Berkeley chapter a year later. At the time, both were called Engineers Without Frontiers. Last year, the name was changed to Engineers for a Sustainable World. Today the national has more than 1,500 members. ESW-B has 50 active members, plus another 200 on its e-mail list.

"We're a new generation of engineers," says Murray, "inspired by the ways appropriate technologies can improve the quality of life for those who are most in need."

But they're hampered by limited funds.

"Our energy is boundless, but not our budget," she says. "And by virtue of the type of work we do, the organizations and community groups that we partner with are also financially strapped. So the burden of travel costs and living expenses for our interns, as well as research equipment and other supplies, falls on our chapter."

Some in the Berkeley community are already pitching in. The Potter's Studio is donating the kiln space for the water filter prototypes. And folksingers Laurie Lewis and Tom Rozum will perform a benefit concert for ESW-B next Tuesday at the Cal Student Union.

Secure credit card donations can be made online at www.esustainableworld.org. Checks can be sent to Engineers for a Sustainable World-Berkeley, Institute for Environmental for Governmental Science and Engineering, 412 O'Brien Hall, #1766, Berkeley, CA 94720-1766.

"Remember," says Murray, "not only can every person make a difference in the world, so can every dollar."