“I have another relative that is a physician, at his graduation many years ago, they said, in the last century modern plumbing added 15 years to American lives”
I would think that the sewer systems (no more out houses) and the modern materials for indoor piping systems, and water treatment systems connected to that were each and collectively bigger factors in that than the plumbers themselves. Once those big systems were figured out, designed, put in place and fell into common usage, learning the “plumbing trade” was a much smaller accomplishment.
I’d ask the son in law about it but he is doing his continuing education for his plumbing license as I type.
I did find this quote.
Dr. Lewis Thomas, medical author and former president of New York’s Sloan Kettering Cancer Research Center, wrote in The Foreign Policy Journal, Spring 1984: “There is no question that our health has improved spectacularly in the past century. One thing seems certain: It did not happen because of improvements in medicine, or medical science, or even the presence of doctors; much of the credit should go to the plumbers and sanitary engineers of the western world.”