In order to remove temporary hardness of water, it is boiled.
On boiling, while Ca(HCO3)2 gives CaCo3(ppt.) , Mg(HCO3)2 gives Mg(OH)2(ppt.).
According to my book precipitation of Mg(OH)2 occurs due to it's high solubility product.
But doesn't a higher solubility product mean a higher solubility? (Since solubility product is the product of solubilities of each component)