Joe Bobst wrote:

We recently moved into a new house with a 3 prong dryer outlet.

The smart thing to do here is replace the 3-prong outlet with a 4-prong, adding
the necessary ground wire from the service panel if needed. With all the
electronic controls and doodads on new appliances these days it makes sense to
get stray currents from static electricity or whatever diverted to a positive
ground muy pronto.
Of course, you could add a grounding wire to any handy metal plumbing if you
are sure there are no plastic piping interruptions in those lines. Your choice,
and good luck.

Joe


It is a violation of the US NEC to use water piping as the ground for a
branch circuit unless it is an underground metal water pipe of at least
ten feet of buried pipe and the connection is made to it within five
feet of were it enters the home.

"250.130 Equipment Grounding Conductor Connections.
Equipment grounding conductor connections at the source of separately
derived systems shall be made in accordance with 250.30(A)(1). Equipment
grounding conductor connections at service equipment shall be made as
indicated in 250.130(A) or (B). For replacement of non€“grounding-type
receptacles with grounding-type receptacles and for branch-circuit
extensions only in existing installations that do not have an equipment
grounding conductor in the branch circuit, connections shall be
permitted as indicated in 250.130(C).
(C) Nongrounding Receptacle Replacement or Branch Circuit Extensions.
The equipment grounding conductor of a grounding-type receptacle or a
branch-circuit extension shall be permitted to be connected to any of
the following:
(1) Any accessible point on the grounding electrode system as described
in 250.50
(2) Any accessible point on the grounding electrode conductor
(3) The equipment grounding terminal bar within the enclosure where the
branch circuit for the receptacle or branch circuit originates
(4) For grounded systems, the grounded service conductor within the
service equipment enclosure
(5) For ungrounded systems, the grounding terminal bar within the
service equipment enclosure

250.50 Grounding Electrode System.
If available on the premises at each building or structure served, each
item in 250.52(A)(1) through (A)(6) shall be bonded together to form the
grounding electrode system. Where none of these electrodes are
available, one or more of the electrodes specified in 250.52(A)(4)
through (A)(7) shall be installed and used.
(A) Electrodes Permitted for Grounding.
(1) Metal Underground Water Pipe. A metal underground water pipe in
direct contact with the earth for 3.0 m (10 ft) or more (including any
metal well casing effectively bonded to the pipe) and electrically
continuous (or made electrically continuous by bonding around insulating
joints or insulating pipe) to the points of connection of the grounding
electrode conductor and the bonding conductors. Interior metal water
piping located more than 1.52 m (5 ft) from the point of entrance to the
building shall not be used as a part of the grounding electrode system
or as a conductor to interconnect electrodes that are part of the
grounding electrode system." Copyright 2002 the National Fire
Protection Association

As you can see the last sentence forbids the use of piping more than
five feet form the point of entry as a grounding electrode or grounding
conductor.
--
Tom H