One shouldn't have the passion regarding this subject. But as someone who can distinctly taste the difference between hard and soft water, I have to write about this!
First and foremost, although some people don't seem to have the ability to taste the difference, hard water tastes awful when compared to soft water. One is chalky and leaves a metallic taste in the mouth while the other is clean, clear, and even slightly sweet.
What accounts for the difference between the two? Well, hard water contains heavy traces of minerals due to contact with them while underground or when travelling from the source to the home. The minerals come from soft rock like limestone, dolomite, marble, and other minerals which over time, dissolves into the water. Soft water, on the other hand, is generally from rain and passes thru pipes.
PROBLEMS WITH HARD WATER
(1) Hard water causes scaling (sticky white scum) which over time clogs pipes, the insides of metal tea or coffee pots, and as I very painfully (to the wallet) found out recently, ruins water heaters.
(2) Regular shampoos don't lather as well in hard water and tends to leave behind salts- resulting in unmanageable hair, especially disconcerting for Asians who go to the US and have never had to use hair conditioner!
(3) Just like your hair, your clothes also retain some of that "hardness" after washing with hard water, thus the need for fabric softeners. Again, something you don't generally need in Asia.
(4) Hard water can cause dry skin to become even drier.
(5) It tastes AWFUL. (I always have to add lemon/lime to mask the mineral taste)
PROBLEMS WITH SOFT WATER
(1) If you have planted tanks like I do and happen to live in Asia where the water is soft- the plants can become rather unhappy due to the lack of minerals, especially of calcium.
(2) Soft water can be acidic- and our bodies prefer an alkaline environment. The minerals in the hard water are actually beneficial to our bodies (but not in too large quantities).
(3) Some soft water is soft due to being treated with softeners.