Distilled Water continues to be the standard of purity when you talk about water at ANY level. Water Stores around the country typically develop a business model called GBB - Good, Better, Best. What they call 'Good' water is filtered water, typical of charcoal filters that Brita sells or many manufacturers sell to screw on your kitchen faucet. Initially a charcoal filter cleans up the taste of water and removes a limited amount of contaminants but very little. The 'Better' water is RO / Reverse Osmosis, which is basically a very elaborate filter system that initially delivers fairly good quality water but over a quick period of time, the filters become clogged and the quality of water drops quickly. The 'Best' Water is fresh Distilled Water and that is why even today all liquid medicines, breathing machines, dialysis machines and many other uses of high quality water ONLY specify distilled water.