Why don't you drink glacier water?

You should not drink glacier water directly from a glacier, stream, or melt pool without treating it first, even though it looks pristine and pure, because it can contain harmful microorganisms, minerals, and pollutants. First, glacier water can contain bacteria, protozoa like Giardia and Cryptosporidium, and viruses from animal feces, bird droppings, and human waste that contaminate snow and ice, causing severe diarrhea and illness. Second, glacier ice and meltwater contain fine rock flour, which is extremely fine glacial silt that can irritate your stomach and intestines. Third, glaciers act like frozen archives that trap decades of atmospheric pollution, including soot, heavy metals, pesticides, and even radioactive particles from nuclear testing, which are released as the glacier melts. Fourth, drinking extremely cold ice water can cause cold shock and lower core body temperature. While some bottled water companies sell glacier water that has been filtered and purified in factories, raw glacier water straight from nature is not safe. National Park Service rangers in Glacier Bay and other parks warn visitors not to drink untreated glacier water. If you want to drink glacier meltwater, you should filter it with a 0.2 micron filter, boil it for at least one minute, or treat it with purification tablets. So the beautiful blue water is not safe to drink without treatment.