[dahfizz]

They use saline because it goes directly into your blood stream. If they used pure water, the osmotic pressure would force water into your cells, causing them to burst (hypotonic).

You can drink pure water because it "becomes" saline as it mixes with the food in your stomach.

Even unfiltered tap water doesn't have very many ions compared to blood or saline solution. Most of your ions come from your food.