We've been visiting France since 1988. The biggest change between our 2010 and our 2012 visits to France was the easy availability of tap water. This was especially true in the provinces, but it was also practical in Paris. I've asked for "de l'eau du robinet" in years past, but it sometimes produced a glance as if I was a madman (or a cheapskate.) In July, 2012, a carafe or wine bottle of tap water was often brought without asking. Although finer restaurants in Paris tried to get us to order bottled water, some Michelin one-stars in Brittany and Normandy had carafes on half the tables. I'd speculate that this is partly the "Green" issue that's now sometimes considered in the USA.
It more has to do with the fact that it's a national law that it must be provided if you ask for it.
Even in 2010 it should have been compulsory to provide tap water. If it wasn't just random chance, I suspect that with the declining economy people are less willing to pay for branded water when they don't have to.
My first trip to France was in 1988. On that trip, and subsequent trips (the most recent was in 2010), I've never had trouble getting tap water just by asking for "une carafe d'eau." I always see lots of people at other tables with carafes of tap water, too. Just my experience. Yours was obviously different - sorry to hear that, and glad you found it better this time.
I'll (kindly) say that it may have had more to do with how you asked for your water. I've never had any trouble getting tap water by asking, as Harold correctly notes, for "un carafe d'eau."
I've also never had problems getting tap water if you ask. Going back as far as the early 90s.
Just returned, we often got a carafe of water on our table even without asking. For the same in Amsterdam we were charged (for a carafe of tap water, not bottled water).
It was so hot in Paris for this last visit that I drank tons of water, and I am not normally a water drinker. I had no problems at all getting "une carafe d'eau" when ever I asked, and in a few places it was brought with our wine /drinks anyways.