About four years ago, when Mark Lotto was a Penn engineering student, his final-project adviser was Arun Deb, a respected water expert. Lotto’s task was to accompany the professor on a trip to India and help him assess some of his initiatives there — like clean water and sanitation for rural schools, and lifesaving arsenic filters for village water supplies.

Of course, the duo made sure the technology worked. But, Lotto recalled, Deb wanted to know about more than that.

For instance, were the people who used the systems taking responsibility for looking after them? Did their governing boards reflect the demographics of the systems’ users — which included not just men but women and students, too? Were the projects financially sustainable? And were the projects’ goals — clean, safe water and sanitation — being adopted by the people who benefitted from the projects in their daily lives?

“Without Dr. Deb, I would have learned only how an arsenic filter works in India,” said Lotto, who works internationally as a product cost engineer for General Electric. “But once I met Dr. Deb, I learned that if you don’t have ownership at the lowest level — if you don’t work with the people who are actually going to use it — then your technology could be the best in the world, but it’s going to fail.”

Simply put, the young engineer learned that technology can be the starting point to changing people’s lives. That’s something that Arun Deb has been doing all his career — and something that this gracious, unassuming man, at age 84, has no intention of stopping.

“I’m grateful God is giving me the opportunity to do this work,” said Deb, a native of India and a resident of Downingtown.

Deb retired in 2003 from Weston Solutions, a West Chester-based environmental consulting and management firm, but has really never kicked back and relaxed. He’s an active board member with Global Water Alliance, a Philadelphia-based NGO dedicated to increased access to safe drinking water and sanitation. He still teaches at Penn, and he has also taught at the University of Notre Dame, University College London, and the Indian Institute of Engineering, Science and Technology.

As such, he’s always mentoring students like Lotto, bringing them to India to see firsthand how environmental engineering can improve life for the world’s needy.

“I can never say Arun’s retired, because he’s always working,” said Stanley L. Laskowski, founder of the Global Water Alliance and a retired Environmental Protection Agency official and Penn professor. “He’s just a wonderful person.”

Raised in the West Bengal state of India in a family of modest means — his father and brothers were schoolteachers and his mother was a homemaker — much of Deb’s water and sanitation improvement work has been focused in the region’s rural villages.

During a visit to India in the 1990s, he learned that villagers were being poisoned by arsenic from drinking contaminated groundwater. What the villages needed, he knew, were arsenic filters in their water systems.

Over the next few years, with the help of the NGO Water for People, which helps people bring clean water and sanitation solutions to needy communities, he embarked on a campaign to bring a filtration project to the villages. With research support from of a local university and $100,000 from the Hilton Foundation, a humanitarian nonprofit, about 200 villages got municipal arsenic filters that helped provide safe water for about 200,000 people.

Part of what made the program sustainable, said Deb, was that organizers formed associations of citizens — which included women — to oversee them instead of relying on the government to manage the projects. As a result, he noted, citizens got used to the idea of helping to fund clean water, instead of expecting water to be free.

The villagers became so proud of their filtration units, he said, that some residents now call them their “temple.”

Another project Deb spearheaded, called WASH (Water Sanitation and Hygiene), brought clean drinking water and sanitation systems such as flush toilets to rural schools in West Bengal. Again, Deb insisted on local oversight, which included students — girls as well as boys.

Yet another project of which Deb is especially proud doesn’t involve water at all — but it, too, is about changing lives.

“For the past 10, 12 years, I’ve been working on women’s empowerment,” Deb said. “In villages, women are generally very neglected. I thought the important thing was education. If women get education, they will get power.”

So Deb has been contributing his own money and working with donors to raise funds for scholarships, books, school supplies, and uniforms for female students at all levels of schooling. Currently he partners with Nishtha, a nonprofit education organization in India, on projects that have helped further the education of about 1,000 students in about a dozen villages.

Said Deb, “I am so proud of these girls,” who are honored in a celebration each year — along with their mothers.

“We realize that mothers have made tremendous contributions,” to their children’s education, he said.

Deb and his wife, Dhriti, a former financial analyst who is also retired, have one child, a son who is a doctor, and two granddaughters: One is a student at the University of Michigan’s dental school and the other is a medical student at Georgetown University. Deb and his wife are proud of all of them.

The couple spends about half the year in the United States, where Deb became a citizen in 1978, and the other half in India, where they enjoy visiting family and friends. But uppermost in Deb’s mind, always, is the development of new, life-enhancing projects. His latest: He’s helping to build a small, rural hospital in West Bengal for poor people.

He has two good reasons to keep his momentum going.

“One is my satisfaction — helping other people,” he said. The other, he added with a chuckle, is more practical. Being retired, he said, “I have to do something.”