It's the simple things.................

      About a decade ago, two Harvard professors, David Cutler and Grant Miller, set out to ascertain the impact of chlorination (and other water filtration techniques) between 1900 and 1930, the period when they were implemented across the United States.  Because extensive data existed for rates of disease and particularly infant mortality in different communities around the country, and because chlorination systems were rolled out in a staggered fashion, Cutler and Miller were able to get an extremely accurate portrait of chlorine's effect on public health.  They found  that clean drinking water led to a 43 percent reduction in total mortality in the average American city.  Even more impressive, chlorine and filtration systems reduced infant mortality by 74 percent, and child mortality by almost as much.
      It is important to pause for a second to reflect on the significance of those numbers, to take them out of the dry domain of public health statistics and into the realm of lived experience.  Until the twentieth century, one of the givens of being a parent was that you faced a very high likelihood that at least one of your children would die at an early age.  What may well be the most excruciating experience that we can confront - the loss of a child - was simply a routine fact of existence.  Today, in the developed world at least, that routine fact has been turned into a rarity.  One of the most fundamental challenges of being alive - keeping your  children safe from harm - was dramatically lessened, in part through massive engineering projects, and in part through the invisible collision between compounds of calcium hypochlorite and microscopic bacteria.  The people behind that revolution didn't become rich, and very few of them became famous.  But they left an imprint on our lives that is in many ways more profound than the legacy of Edison or Rockefeller or Ford.

-Steven Johnson,  How We Got to Now:  Six Innovations That Made The Modern World