AS THE PRESIDENT of the Massachusetts Taxpayers Foundation, I spend a lot of time considering ways to reduce health care costs.  In my opinion, the best way to reduce health care costs is not to incur them at all. A well-functioning public health system can be an effective tool for reducing healthcare costs, improving the health and extending the lives of Massachusetts residents by protecting them from a wide variety of health threats, from drinking water contamination to food poisoning and infectious disease. By investing in this kind of prevention, we can make our communities safer and avoid unnecessary healthcare costs.