I have a report from the American Water Works Association on Corrosion from Electrical Grounding to Water Pipes. Very little corrosion is caused by AC, but almost all from DC, due to hair dryers, drills, etc. The DC can flow away or toward the pipe. If away it will cause loss of metal.If the water line is metallic to the water maint, then a short section of NM pipe past the ten foot section (250.52A 1) will stop most of the corrosion
I also have a 1945 study by the IAEI and AWWA that says no corrosion from grounding.