Hard water is not equal to water with heavy metals

No health-based guideline value is proposed for hardness in drinking water. Excessive hard water can also have corrosive tendencies. Naturally soft water can have aggressive properties towards the piping material through which it is distributed…resulting in the presence of certain heavy metals, such as cadmium, copper, lead and zinc, in drinking water (National Research Council, 1977)

(Ferrante, M., Oliveri Conti G., & Rasic-Milutinovic Z. (2014). Health Effects of Metals and Related Substances. London: IWA Publishing)

Metal pipe corrosion is a continuous and variable process of ion release from the pipe into the water.

(http://www.cdc.gov/fluoridation/factsheets/engineering/corrosion.htm)

Hard water is a very common problem, affecting water in more than 85% of the country. It is a result of the dissolved minerals calcium, magnesium and manganese…While these are all unpleasant effects, hard water is not a hazard to human health and can be treated.

(http://extoxnet.orst.edu/faqs/safedrink/hard.htm)