Grounding your mast and the coax shield to a separate ground rod does not meet the code requirements of the NEC unless the ground rod is connected (bonded) to the house ground with 6 gauge copper wire.
However, the code is only a suggestion. The local AHJ (authority having jurisdiction), who is usually the electrical inspector, has the final say. His interpretation of the code becomes the local law, and is binding on you and the local electricians.
The purpose of bonding the ground rod to the house ground is to eliminate any difference in potential between the two for electrical safety.
I'm not an electrician, but my personal opinion is that if the cold water pipe meets the local law for the house electrical service, it should be suitable for your antenna system.
But, it's your antenna system and your choice.
If the antenna is outside, the coax shield should be grounded with a grounding block that is connected to the house electrical system ground with 10 gauge copper wire for electrical safety and to reject interference. For further compliance with the electrical code (NEC), the mast should also be grounded in a similar manner to drain any buildup of static charge which will tend to discourage a strike, but the system will not survive a direct strike.
Another viewpoint:
http://www.reeve.com/Documents/Artic...quirements.pdf
another opinion:
http://www.dbsinstall.com/diy/Grounding-2.asp
The latest device to connect other services to the house ground is the IBTB. It has a lay-in connection for the house ground wire so that it is not necessary to disconnect the house ground to make a connection. Disconnecting the house ground, even for a moment, isn't safe. In the past, a split bolt has been used to connect to the house ground wire.
Based on my personal experience, grounding the coax shield to the house ground with a grounding block is the most important, because I have had three close calls with electrical shock.
The coax is connected to AC operated equipment. If that equipment becomes defective, you can be exposed to shock from leakage current if the coax shield isn't grounded.
see also
http://www.hdtvprimer.com/antennas/basics.html
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