The grounding electrode conductor needs to be unspliced or spliced with a non reversible device but you can have a tap to a secondary electrode with any approved chapter 3 device as I read it.

Quote
The tap conductors shall be connected to the common grounding electrode conductor by exothermic welding or with connectors listed as grounding and bonding equipment in such a manner that the common grounding electrode conductor remains without a splice or joint.


If you are hitting a water pipe you need to do it within 5' of the entrance.

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Greg Fretwell