I'll start off by telling you a secret. Many years ago as a child, my dream was to become a physician. The power to intervene directly and transcend people's lives through improving their health, to the eyes of a mere boy, seemed the most exciting of all careers.

Yet circumstances that followed led me down another path, and I became an environmental engineer instead, working for the city of São Paulo for a number of years in the area of drinking water supply. There was much to be done and my hours were full. Still, my frustration remained. What would my life have been like had I fulfilled my original dream?

As often happens, the strange forces of destiny one day brought me face-to-face with the general manager of a rural water supply agency in the People's Republic of China. Dr. Li was a chap at that time way into his 70s, and responsible for bringing water to one billion Chinese. Through the interpreter I learned, to my great surprise, that he was a medical doctor. Keenly curious, I inquired why someone of his stature would dedicate his career to water supply. His answer embodied all the wisdom and simplicity that were the fruits of selfless, lifelong public service.

"As a physician, working very hard, I could at most contribute to the health and well-being of some two dozen people a day. Whereas my responsibility for rural water supply allows me the good fortune of responding to the needs of a billion people on a daily basis."

The resonancy of his words unleashed a passion for my career that I had not known until now. They opened my eyes about the impact of the physical environment on human health and on our feelings about life in general. I'd found a way to connect my original dream with my professional reality. I chose to become a public health engineer.

I believe we are all born with a special dependency upon our surroundings, and particularly on the availability of natural resources. Indeed, we come to this earth utterly lacking in the basics to guarantee survival.

The consumption of natural resources is an inescapable part of life. So is the disposal of waste from human activities back into the environment. And while "borrowing" from the environment assures life, environmental abuse creates imbalance, increasing the risk of disease and possibly even death.

The physical environment is a living entity with a capacity to recover from mild "aggressions", just as the body heals its own wounds. For example, the cutting of a few trees is rapidly compensated for by new growth and is unlikely to have any impact on the availability of oxygen for our respiration. But there are other types of aggression that alter environmental makeup to such a degree that its self-regeneration mechanisms are compromised. Essentially this occurs whenever we disregard nature's threshold for degradation and absorption, such as in the cases of unrestrained deforestation and waste dumping. A destructive relationship of this type defeats the raison d'étre of our environment: to provide the raw materials necessary to support life and promote good health.

As a public health engineer, now I could appreciate the doctor-patient interdependency relationship on a much grander social scale: if each individual were to pledge his or her participation toward nurturing and protecting the environment, then as communities and nations we could make a major contribution to everyone's health and well-being.

We start by rethinking individual relationships with our surroundings. To conserve natural resources--food, water, fuel--is within everyone's capacity and interest, and could easily become a daily concern. Do we really need to produce two pounds of garbage every day? Couldn't we avoid using our cars as extensively as we do? Using 200 gallons or more of water every day, as many of us do, is certainly an exaggeration, when 80 to 100 gallons would suffice for most of us.

Such seemingly innocuous aggressions as these are rapidly diminishing nature's ability to provide the vulnerable and unprotected human race with the basics for survival. On the other hand, striking a harmonious balance between our biological needs and egotistical wants--while there's still time--imbues the environment with an inherent sustainability and offers continuity to tomorrow's unborn generations.

In our homes and families, we can all become environmental engineers. As communities and nations, we have the potential of a Dr. Li to reach billions of people with a life-transcending message. Is there any good reason to wait?