Water is naturally soft when it falls to the ground as rain. Depending on where the rain falls will depend on whether it will stay soft or become hard. The rain that sits on or travels through or across hard rock like granite stays pretty much unaffected in terms of natural mineral content. While rain that percolates through softer rock structures like limestone will dissolve mineral salts like calcium and magnesium increasing its hardness and along with many trace elements, its taste and flavour. The taste of chlorine associated with drinking water in the UK is not naturally occurring and is added by your water supplier.