Should data ground wires be attached to plumbing?
National Electrical Code 2014
Chapter 8 Communications Systems
Article 800 Communications Circuits
IV. Grounding Methods
800.100 Cable and Primary Protector Grounding.
(B) Electrode. The grounding conductor shall be connected in accordance with 800.100(B)(1), (B)(2), or (B)(3).
(1) In Buildings or Structures with an Intersystem Bonding Termination. If the building or structure served has an intersystem bonding termination as required by 250.94, the grounding conductor shall be connected to the intersystem bonding termination.
(2) In Buildings or Structures with Grounding Means. If the building or structure served has no intersystem bonding termination, the grounding conductor shall be connected to the nearest accessible location on the following:
(1) The building or structure grounding electrode system as covered in 250.50
(2) The grounded interior metal water piping system, within 1.5 m (5 ft) from its point of entrance to the building, as covered in 250.52
(3) The power service accessible means external to enclosures as covered in 250.94
(4) The nonflexible metallic power service raceway
(5) The service equipment enclosure
(6) The grounding electrode conductor or the grounding electrode conductor metal enclosure
(7) The grounding conductor or the grounding electrode of a building or structure disconnecting means that is grounded to an electrode as covered in 250.32
(3) In Buildings or Structures Without Intersystem Bonding Termination or Grounding Means. If the building or structure served has no intersystem bonding termination or grounding means, as described in 800.100(B)(2), the grounding conductor shall be connected to either of the following:
(1) To any one of the individual electrodes described in 250.52(A)(1), (A)(2), (A)(3), or (A)(4)
(2) If the building or structure served has no intersystem bonding termination or has no grounding means, as described in 800.100(B)(2) or (B)(3)(1), to any one of the individual electrodes described in 250.52(A)(7), and (A)(8) or to a ground rod or pipe not less than 1.5 m (5 ft) in length and 12.7 mm (1/2 in.) in diameter, driven, where practicable, into permanently damp earth and separated from lightning conductors as covered in 800.53 and at least 1.8 m (6 ft) from electrodes of other systems. Steam or hot water pipes or air terminal conductors (lightning-rod conductors) shall not be employed as electrodes for protectors.

800.100(B)(1)
An Intersystem Bonding Termination can be either a set of terminals securely mounted and electrically connected to the meter enclosure, a bonding bar near the service equipment enclosure, or a bonding bar near the grounding electrode.  These terminals are specifically for bonding and grounding of communications and other &quot;intersystem&quot; circuits.
If this exists, the telephone and dish should be bonded using these terminals.
800.100(B)(2)
If an Intersystem bonding termination does not exist, this section provides a list of acceptable alternatives. Included in the list is the &quot;interior metal water piping system&quot;. Which can be used as long as the connection is within 5' (1.5 m) of the point of entrance, and the piping is in direct contact with the earth for 10' (3 m) or more (250.52(A)(1)).
800.100(B)(3)
This section gives even more alternative bonding locations, and again points to 250.52(A)(1) Metal Underground Water Pipe..

tl;dr
Bonding to the water piping system may not be a problem, as long as the termination is within the first 5' of the pipe entering the building and the pipe is in direct contact with the earth for 10'.  However, if the dielectric union is not conductive, there should be an appropriately sized bonding jumper connecting the two sections of pipe.
If you're worried about it, or you're having problems. You could move the bonding terminations to the other side of the dielectric union, use an alternate bonding method, or install an intersystem bonding termination and use that.