Yep, if all the water lines are metallic throughout and with multiple grounds at the xfmr and each house, there's bound to be some current flowing on the pipes. How much will depend upon the relative resistances.
We have a similar situation in the U.K. with our PME distrubution system, which is basically the same as the standard U.S. arrangement as far as grouding goes.
In fact the very presence of currents on the pipework with this system resulted in our "code" ruling that a different grounding arrangement must be used in the supplies to gas stations and other similar plants.
