From the Source

The first time I walked by the little park on Avenue Victor Hugo just shy of Avenue Henri Martin in the 16th arrondissement, I was baffled by the sight of an older lady toting a suitcase caddy laden with a plastic crate full of water bottles.  She appeared to be filling up her two liter bottles at the park's pump.  "That's odd,"  I thought.  "Does city water really cost so much that folks on fixed incomes are reduced to getting their water this way?" 

Only much later did I find out that the pump at Square Lamartine is connected not to city pipes but to a spring of naturally pure water.  There are two other such sources in Paris:  one at place Verlaine in the 13th and another at place Hebert in the 18th.  The one in the 16th has a particularly interesting history.  While the current well dates back to the works of Baron Hausmann in 1855, the area was well known for its healing waters much earlier.  Benjamin Franklin, who lived in Passy during his years as envoy from the nascent American nation to the French court, was said to have returned to the U.S. with a stash of barrels containing the spring water.

Personally, I'm not too picky about my water so I can't tell you how Lamartine water rates against Evian, Volvic, Cristaline or any of the other 200 some brands of water marketed in France.  Or for that matter, I have no idea how it stacks up against what comes out of the tap.   If you really want to know, hop on the 63 bus or metro line 9 (rue de la Pompe) and check it out for yourself.  Just be sure to bring your own bottle!