Given the increase in concern over the purity and safety of bottled water, many people have asked the following question: How Can I Tell if the Water I Purchased Started Out As Tap Water?
The folks over at WebMD explored that question recently and had this to say:
Roughly 45% of the water sold in single-serve bottles comes from a municipal water source.
By law, bottled water that comes from a municipal water supply has to disclose this on its label unless the bottler takes steps to further purify the water, which most do. In this case, the label will say “purified water” or “purified drinking water,” but the original source is probably tap water.
Water labeled “spring water” comes from an underground water spring, but it may be piped to the bottling plant.
“Mineral water” comes from an underground source and must contain no less than 250 parts per million total dissolved solids, such as salts, sulfur compounds, and gasses. No minerals may be added to the water by the bottler.
“Artesian water” or “artesian well water” must come from a well that taps a confined aquifer. (source)