Interesting, I hadn't really considered the hardness of the water.
Here at home we have water that is medium to hard, with CaCO3 at 300ppm, and I stick with Mitchell's Wool Fat shaving soap and the safety razor:
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However for years I have traveled a lot for work, so end up shaving using different water in different countries, and sometimes even different continents. The brush, razor and the shaving creme remain the same, as for travel I take them with me - using a razor handle (bought from here) that takes disposable multi-blade heads. I can't honestly say that I've ever really noticed much difference in terms of the lather generated.