Continuity means little, conductivity means everything. Just how much conductivity is there in sprinkler pipes?
Here is something from long ago concerning this issue.
QUESTION: "We are installing a fire sprinkler system in an apartment building using NFPA 13R criteria. The electrical contractor is attempting to place a bonding wire at the base of the sprinkler system riser and connect to the neutral bar in the main electrical fuse panel, then connect to the building ground rod. Can the electrical bonding wire at the base of the fire sprinkler system violate NFPA 13, paragraph 5-14.4.3.5, and what detriment to the fire sprinkler system will result if the electrical bonding is allowed to remain in place?"
ANSWER: In response to your question, we have reviewed NFPA 13, NFPA 13R, and NFPA 70, 1999 editions, as the applicable standards. Our informal interpretation is that using the fire sprinkler system piping as a grounding electrode is prohibited by NFPA 13; however, NFPA 70 requires interior metal piping to be bonded in some situations.
NFPA 13R does not address this issue nor does it refer the user to NFPA 13. However, in good practice the user should refer to NFPA 13 and other applicable standards for guidance. There are two reasons for connecting a conducting wire from the neutral bar of an electrical panel to sprinkler system piping. One is where the sprinkler system is intended to be used as "grounding electrode" for the electrical service. This is prohibited by 13:5-14.4.3.5. The other is where the sprinkler system has the likelihood of becoming energized and "bonding" is necessary to prevent the occurrence of an electrical potential difference between the sprinkler system piping and other conductive material in the building. This bonding requirement is given in NFPA 70, paragraph 250-104©. It is important to note here that if the sprinkler system is not connected to other electrical equipment, conductors, etc., it is unlikely that the piping will become energized; thus bonding is not required. FPN to paragraph c indicates that bonding all piping and metal air ducts within the premises will provide additional safety.
Using the sprinkler system piping as a grounding electrode is prohibited by NFPA 13. This is to prevent degradation of the piping resulting from electrolysis. Bonding the sprinkler system may result in electrolysis and subsequently degradation of the piping only in the presence of stray or leakage currents. Examples of these events include high voltage crossover between high- and low-voltage systems, lightning strikes, voltage induction, and electrical equipment insulation failures. The degree to which the piping will degrade is difficult to predict. The exact effect depends on numerous variables like soil conditions, electrical system integrity, event voltage and duration, etc. Also, there are methods to protect the sprinkler piping from stray currents. For example, installing a dielectric (nonmetallic) fitting between the overhead sprinkler piping and the underground supply piping will prevent stray ground currents from entering the overhead piping. Also, if the dielectric fitting is used, the sprinkler system piping loses its grounding electrode capabilities.
In summary, using the sprinkler system piping as a grounding electrode is prohibited. Bonding the sprinkler system piping is only required when it may become energized.
Personally I do not bond or connect anything to the sprinkler line and will spend hours teaching an inspector just why I don’t.