Will give brainliest! why does it make sense that kidney stones or cardiovascular disease could be related to hardness in water?

Hard water is not considered a health hazard. However, it has been stated by the National Research Council that hard drinking water usually donates a small amount towards entire magnesium and calcium in the human dietary requirements.  

They further state that in some of the cases, where dissolved magnesium and calcium are very large, water could be a prime contributor of magnesium and calcium to the diet. However, very high hardness, that is, above 300 ppm that is not usual of drinking water arising from surface water, may be related to the higher threat of kidney stones and cardiovascular diseases.  

In the majority of the cases of kidney stones, the blood in the body of human being, due to some kind of inherent issues, begins to absorb more calcium from water and food that is in the real sense required. As a consequence, the extra amount of calcium gets deposited on the walls of the kidneys in the process of excretion.