I think there is something to the water idea, but not exclusively. How the water interacts with the hair+the additive (in this case the particular soap being used) is something I have noticed over the years because I travel a lot. But with detergent based shampoos it is less obvious, to almost impossible to notice. With sodium bicarb it was extremely noticeable when I traveled; so much so that my hair felt dirty when washing with water in some other municipalities. I don't think I recall traveling much during my brief encounter using lye soap on my hair, though, so I am unsure of how much of a difference I may or may not have experienced when I used different water with lye soap. My hair is pale, fine and straight. It was below my waist and had not been cut in over 10 years when I went through my lye shampoo experience that turned it to the texture of straw.
Although you and I are both in Illinois, it is possible we have similar water, but also possible we have totally different water, depending on our locations. IMO, it's more about our probably hair differences (which is determined by genetics). But for the sake of argument, our water is something along the lines of 'city water' (we don't live in a city, but it's not well water and it does come from the town's water supply) but the pipes are very old and the method of 'cleansing' the pipes seems rather archaic to me, but shows how much build-up occurs in our pipes (the water comes out an ugly horrible yellow for a few days a couple of times a year when they 'flush out' the system - so much so that people are warned not to wash whites.) Perhaps larger municipalities (our population is about 6,000 people and it is a rural farming community) would possibly have water with fewer impurities. Our water is full of various minerals that I find make drinking it pretty unbearable, so we use a water filter on our drinking faucet, but that is the only water that is filtered.
