Galvanic corrosion is the result of two dissimilar metals coming into contact with each other with a DC current applied. Where is this taking place with the water heater? If you say in the connections to the water heater then I will say that the brass union that would be used would make for continuity.
If you say that flex is being used to connect to the water heater I am going to say that the flex will do either one of two things. One it will maintain continuity or two it will not. If the flex maintains continuity then why do anything more? If the flexible connection is not metallic then where are the different metals coming from?
You are correct that the word THE means the metal water piping and the word the is singular meaning the water pipe not those water pipes. Is it possible to have more than one metal water piping systems in a house? Yes, there is the potable water system, waste water system, gray water system, and let’s not leave out irrigation which could be part of the potable or gray water systems. I have even saw metal water piping systems installed for heat. Each of these metal water piping systems will require that THE bonding conductor is installed.
Instead of reading articles in magazines and looking at the picture they have there I go straight to the horse’s mouth when I am doing research on these debatable subjects. Here is a proposal that has the panel statement on it, yes the code making panel charged with voting on the proposals or one could say the words of those charged with writing the code. What is something that any electrician can do to see if a metal piping system of any type is made completely from metal? Would a continuity test do the job?
5-236 Log #2432 NEC-P05 Final Action: Reject
(250.104(A)(1))
____________________________________________________________
Submitter: Robert P. McGann, City of Cambridge
Recommendation: Revise text to read as follows:
Metal water piping system(s) that is likely to be energized, installed in or attached to a building or structure shall be bonded.
Substantiation: With much expanded use of plastic water piping system(s) isolating section of metal piping systems. This type of installation leaves contractors and inspectors what is required to be bonded.
Panel Meeting Action: Reject
Panel Statement: The requirements of 250.104(A) apply to
complete metallic water piping systems. Where there is no complete metallic water piping system, then the requirements of 250.104(B) would apply for those portions of isolated metal water piping system likely to become energized.
Number Eligible to Vote: 15
Ballot Results: Affirmative: 15
See page 220 on this link.
http://www.nfpa.org/assets/files/AboutTheCodes/70/NEC2008ROP.pdf
Now you can see that it is not only my opinion but the opinion of those who write the codes that the bonding of hot to cold is not required by the NEC but any bonding jumper installed is required to land at one or the other places outlined in 250.104(A)(1) even if the claim of galvanic corrosion is the purpose of the bond.