Hard water can also clog plumbing and make water taste bad. Not only are calcium and magnesium protective of the cardiovascular system, but soft water causes more lead and cadmium to leach out of pipes. Water softening devices typically use ion-exchange resins to replace calcium and magnesium with sodium, which can raise blood pressure. Some brands of bottled water studied by the Toronto Public Health authorities had less aluminum, lead and nickel than tap water, but more barium and cadmium. Glass bottles can release heavy metals into water.
Distillers accumulate hard residues, primarily composed of calcium and magnesium.
Activated charcoal filters remove chlorine, organic chemicals and pesticides, but not fluoride, nitrate, lead or other heavy metals. Because activated charcoal removes chlorine, these filters can breed bacteria. To prevent this, carbon filters are often impregnated with silver, which kills bacteria. Silver is toxic to humans as well, so one must be careful to not buy a unit that releases too much silver into the water. The most effective units are those which combine reverse osmosis with charcoal filtration.