“X percent of the world’s population still don’t have access to clean, drinkable water on tap. Y percent of all the people who ever lived in the 20th century didn’t have this.”
I’m trying to establish the right percentages to slot in for ‘X’ and ‘Y’. Or, if exact figures are never going to be possible, I’d like to at least establish credible, plausible numbers backed up by some citable source(s).
When I refer to potable water ‘on tap’, I mean either in your home or very nearby, so that (as in the UK or all of the USA I know of) it is so easy and convenient to access drinking water at any time that it’s easy to take it for granted. Bottled supplies don’t count.
My point is to underline that something so important, that it’s so easy to take for granted, is actually something of a miracle of technology, engineering and infrastructure; one that many, many people in the world and in history either do not have or did not have.
You also want to define “drinkable”. Many places have running water systems with pathogens that the locals have all gotten used to, but which will wreak havoc with tourists.
Obvious problem with your second statement: does it count if a person lived their whole life without running water but then got it in the last few years of 20th century? What if they lived mostly in the 19th century and never had it in the 20th either?