You must BOND the interior metal water piping system based on table 250.66 according to 250.104(A)(1) EVEN if the building is fed with PVC water pipe.
Exsample: If a one family dwelling has a 400 amp service that is fed with 600MCM AL service entrance conductors, then the bond to the metal water piping must be 1/0 copper based on table 250.66
Well, if the dwelling is completely piped in PVC water pipe, then there isn't anything to bond as instructed by 250.104(A)(1)
Other metal piping systems must be bonded according to table 250.122 useing the rating of the OCPD likely to energize the piping.
Exsample:The dwelling's water pipe is all PVC...but the plumber installs the forced hot water piping with copper from the oil fired boiler which is fed by a 15 amp OCPD, well then the equipment grounding conductor run with the circuit conductors is what you would use for the bond(#14).
If that whirlpool tub is fed with copper water pipe,then bond the motor to the piping under the tub with #8 solid.If it is fed with PVC pipe then there isn't anything to bond.