I think hard water is 'natural' water from eg rivers and rain and soft water is treated water like from the tap... don't quote me on this.. I might be wrong!
All of our water comes from rain. If the rain has to percolate through limestone type rocks then some of the limestone dissolves and you get hard water - water which contains calcium (and possibly) magnesium ions which form a scum with soap. If the underlying rocks are insoluble then the water tends to be soft. Water ehich flows from the Pennines tends to be hard; the west of Scotland, where I live, has very soft water.