This actually makes a lot of sense.
Until three months ago i was located in Munich, where the water had an extremely high mineral content, to the pint where I was forced to use bottled water for my espresso machine, as the tap water just clogged the system. I am now in the Netherlands, where the water is very soft and I have subsequently noticed vastly different results in the lather that all of my soaps create.
It really depends on the water as most hard water is higher in alkaline content. Not necessarily acidic but it does affect lathering and potentially the durability of the blade's edge.
I live in a hard water area and do Get a really good lather, usually getting a max of 4 shaves per blade.GSB blade and SV soap.
Recently I went on holuday to a soft water area, and the lather was noticeably better by a good margin. I used the same blade for ten shaves with no feeling it needed changing.
I wonder if ,in a hard water area, a minute layer of limescale builds on the blade making it less effective. Maybe if you washed and dried the blade after each shave , it would last considerable longer.
I aways rinse my blade/razor disassemble it and make sure there is no residual soap on the blade before I pat it dry and reassemble the razor once it too has have wiped dry.
This is not only to try and extend the life of the blade / razor but to make sure I don't shave with a dirty blade.
Happy shaves,
Mawashi