100% natural pure water is difficult to find in nature. As soon as rain hits the ground, it becomes mineralised. Humans have been drinking mineralised water since they existed on earth. If water is demineralised by reverse osmosis or distillation and we drink it, will this be something the body is not used to? Will it do us any long-term harm?
The debate has been running for a long time. If you look at the "The Natural Mineral Water, Spring Water and Bottled Drinking Water Regulations (England) 2006", the minimum hardness concentration in water sold to the general public must contain a minimum of 60 mg/l calcium. However, hardness consists of a complex mix of polyvalent minerals, the main component of which is calcium. Is adding a calcium salt to RO or distilled water up to 60 mg/l the same thing? Probably not.
The reason often given for the need to maintain a minimum of 60 mg/l calcium is a body of epidemiological evidence that hardness in water has a benefit to cardiac health. Does this infer that the absence of hardness salts could damage cardiac health? Since the 2006 publication, the debate has continued over the years, with involvement of the Food Standards Agency, the WHO, The Scientific Advisory Committee on Nutrition and the bottled water industry, to mention a few.
A number of health aspects of water with or without hardness salts have been considered, including osteoporosis, hypertension, stroke, insulin resistance and epidemiological studies of water hardness (or lack of it) and cardiovascular disease. These assessments are on-going and until a definitive conclusion is reached, water for human consumption, treated by osmosis or distillation, remains regulated at a minimum of 60 mg/l calcium re-mineralisation.