David Zwick was a student at Harvard Law School in the early 1970s when he joined a group of promising attorneys working with consumer activist Ralph Nader. He wound up heading a groundbreaking study of the nation’s water pollution and launching the first grass-roots clean water movement.

Zwick’s research and organizing are credited with spurring passage of the Clean Water Act of 1972 and the Safe Drinking Water Act of 1974. He also was the founder and longtime president of Clean Water Action, an environmental advocacy group with chapters around the nation.

Zwick, 75, died Feb. 5.

“He was the most consequential advocate for clean water and for mobilizing grass-roots efforts combating local water pollution in 45 years,” said Nader.

Nader described Zwick as charismatic, hardworking and “one of the unsung heroes of our time.”

Zwick was born May 1, 1942, in Rochester, N.Y. He earned a bachelor’s degree from the U.S. Coast Guard Academy in Connecticut in 1963, and then served four years as a Coast Guard officer, including 18 months in Vietnam. He went on to earn a law degree and a master’s degree in public policy from Harvard University.

In 1971, Zwick co-authored a book based on his research with Nader, “Water Wasteland.” The next year, he co-authored the bestselling “Who Runs Congress?”

Zwick’s activism coincided with the dawn of the environmental movement. The first Earth Day was in 1970, and the unregulated pollution in the nation’s air, land and waterways was gaining the national spotlight.

“If there was something important happening in the environmental movement during those early days, Dave Zwick was part of it,” said Rep. Frank Hornstein, DFL-Minneapolis, a former co-director of the Minnesota chapter of Clean Water Action. “And he knew we needed local people involved.’’

Zwick devoted himself to grass-roots organizing, including door-to-door canvassing, to inform citizens and change government policies. It was a new approach in the environmental movement back then, Hornstein said.

“He recruited and trained a lot of people who went on to do environmental work,” said Peggy Ladner, who worked with Zwick at the national office and when Clean Water Action opened its Minnesota office.

“He amassed a small army of mainly young people,’’ said Ladner, now director of the Nature Conservancy in Minnesota. “He wanted to inspire folks and give them an opportunity to grow in their jobs.”

Zwick spent most of his career as the national president of Clean Water Action, setting up chapters around the country, often moving to get them off the ground, said his former wife, Wendy Weingarten Zwick. He shaped Clean Water Action into both an environmental advocacy group and a vehicle for campaigning for like-minded candidates and issues, she said.

The couple and their three children, who had been living in Washington, D.C., moved to Minneapolis in 2005. Zwick retired from Clean Water Action in 2008 and started a nonprofit called Base Builder LLC, that helped other progressive groups nationally create canvass campaigns and fundraise.

At the national office where Zwick worked for years, a tribute to him was posted last week. One part reads: “Our [nation’s] water is more fishable, swimmable and drinkable today because of David.’’

Zwick is survived by Weingarten Zwick and three children, Winnie, Ruth and Jack. A memorial service will be held Friday at 11 a.m. at First Universalist Church in Minneapolis.