The benefit to human health that water quality and proper sanitation has is marked.  The attached article offers some significant relevant insight.

Public health  may be defined in broad terms as "All organized public or private measures to prevent disease, promote health, protect people and prolong life among the population. Its activities aim to provide conditions in which people can be healthy and focus on entire populations Thus, public health is concerned with the total system of health and health care rather than individual persons per see.                         Civil engineering is a major contributor to the success of public health.

Also if we look at this definition of the concept of environmental health "The totality of elements, factors or conditions in the surrounding of man that can affect the human health and well being positively or negatively. These might be physical (heat, radiation), chemical (pesticides, industrial wastes), biological (viruses, bacteria) or socio-cultural (smoking, drug abuse, social  relationship).

Civil engineering is of course the major contributor in the physical aspects of environmental health particularly in city planning, water supplies and sewage disposal. Thus it is a significant contributor to the health of people. However, this does not mean that civil engineers are more influential than the entire medical profession. The link of health to environment is supposed to be mainly identified by medical people.

Personally, I disagree. Civil engineers design structures that are safe to the environment and do not negatively impact on the public health, but the medical profession has a far greater role on ensuring public health is safeguarded. Civil engineers are not health professionals. What can be said about civil engineers can also be said about other engineers or even other professionals - whatever we do, the public health and safety must be taken into consideration in all our decisions.

The British Medical Journal asked their readers what innovation had had the most impact over the past 2 centuries and Public Health Engineering (water supply and sanitation) got the most votes.

There is also evidence (see Thomas McKeown) that most of the historical drop in life expectancies occurred before all the current medical innovations like vaccinations and antibiotics.

So the claim has a reasonable basis, over the long term but, today, we take the benefits for granted and medical science is providing some further (relatively small) improvements in big indicators like mortality rates and life expectancies.

I think the core business of medical practitioners is to respond to the lack of public health by intervening as needed to restore a certain level of health standard in the community.  Other professionals collectively contribute to provide what is needed in terms of infrastructures and services to establish reasonable living standard and healthy environment for the community. Of course, medical practitioners do contribute as well (in terms of health information) in the process of creating such environment.  In summary, you cannot single out one profession as better than the others when it comes to public health.

In order to answer this question, the question and hypothesis must be analyzed in two ways. The first concerns the engineering profession and the second relates to the medical profession. Then, a comparison is made between the effect of both professions on public health.

1 - As for civil engineers, their impact in design is limited to the psychological aspect of public health in terms of quality of design and colors used, and that this aspect of great impact, either physiological and physical and the effects of diseases, the impact of civil engineer few.

2 - The medical practitioner, through the diagnosis distinguishes between the psychological and physiological aspects, in light of each subject is subject to the treatment that suits him.

In the field of humanities, both answers are correct and can not be ascertained

Interesting question. Let me add one: who saves more lives (or happy life years): teachers or physicians? A question I would be very interested in exploring.