You are right. The right balance of Calcium, Magnesium, Sodium and Potassium is important for preventing heart disease and cancer.
And we do get a lot of minerals from water. So drinking de-mineralized/soft water is "unhealthy" . Thats one reason, I decided NOT to buy a water distiller.
But what should be the ideal Sodium:Potassium and Calcium:Magnesium ratio. I have read that Na:K ratio should be something like 9:1 and Ca:Mg should be like 1:1. Does that look right to you.?