If anything goes wrong and the pipes become energized the breaker will now trip because your piping system is BONDED to the electrical system's grounded neutral. Without this BOND the pipes would STAY energized.
A "ground" as in the sense of a ground rod or water pipe electrode is NOT a safety ground. At lease not in the sense of a ground that will trip a circuit breaker.
Meaning if you sink a ground rod outside and hook it up to an ungrounded receptacle, and there is a short to ground, the breaker will NOT trip. It will simply send current into the ground and bring up worms at best and kill someone at worst.
The "safety" ground in your house is the neutral bond in the main panel.