The World Health Organization has a report titled "Health risks from drinking demineralised water". The main problem is that water without minerals upsets the osmotic balance and leads to lysing (rupture) of the cells lining the stomach.
The WHO has moved stuff on their site, but I think this document is one source:
The WHO has moved stuff on their site, but I think this document is one source:
http://www.who.int/water_sanitation_health/dwq/nutrientschap...
Coffee grounds are a good filter for removing heavy metal contaminants from water:
http://www.nytimes.com/2016/09/24/science/coffee-grounds-fil...