Sparky,
For the water pipe, it doesn't matter if you are using it as a grounding electrode or just bonding it. The conductor is sized by the size of the service entrance conductors and Table 250.66. Fo a 200 amp service, #4 is the miminum for the connection to the water pipe and if your service entrance conductors are larger than 3/0 you would have to use a #2. The connection to the ground rod is never required by the code to be larger than #6. See 250.66(A).
