[pessimizer]

Every reason mentioned except the main one - that you can't charge $4 for a cup w/tap water in it? Also when fast food/day-to-day restaurants give you a cup for water, it's tiny and uncovered.

I would prefer tap water in all cases. It is never a convenient choice.

edit: If you wanted to legislate effectively (rather than in a Bloombergian manner), just require that tap water be a first class citizen at restaurants (same cups, same sizes), and that the purchase of soda/bottled water cannot be involved in a package discount, unless tap water would give you the same discount.