Assuming the hot and cold plumbing is mostly metal pipes.

If possible run more than one ground connecting wire in two or more
different directions. Even long, bent wires are far better than none. If
possible also include a wire to a cold water pipe. Run wires unobtrusively
under carpets, etc. 18 gauge to 14 gauge, bare, enamelled or plastic
insulated wires will do fine.

Don't forget all the mains wiring in the building (and equipment connected
thereto) is also connected to your radio and form part of its ground system.
Every bit of stray inductance and capacitance adds to its lectrical bulk.

Make as much use as possible of the large set of random, cross-connected,
terminated radials in the building. In principle, you have at your disposal
one of the best ground systems for miles around. Connect directly from the
transmitter to it as often as you can.

High voltages between pipes and wiring and nearby equipment are very
unlikely to exist because of the large electrical mass of the whole. And it
is impossible to put one bare foot out of the window to reach the real
ground while turning on the cold tap with your bare hand in the bathroom.

To be absolutely safe start with low power before attempting 100 watts.
Don't exceed 100 watts. I say this simply because I've never used more than
100 watts myself when using the plumbing system as a ground. Never had any
trouble with RF burns. Not even tingling. You and the transmitter are
inside a sort of random Faraday cage.

If an occasonal interference to TV is a problem tackle it from the TV set
end.

Problems, if any at all, get better the lower the frequency. There may be
only one band affected. So avoid it. I've never heard of a problem on
160m. And problems do occasionally arise whatever the ground system when
used with an end-fed wire. Or even with an HF rotateable beam fed over a
balanced line.

With a high random 100 foot wire out of the window, plus a tuner, you will
do very well. By extending the end downwards to make 140 or 150 feet you
will do even better.

The only unavoidable problem lies in the locally-generated noise level at
the lower frequencies.
-----
Reg, G4FGQ

======================================

"Rich" wrote in message
om...
Hi all. I'm sitting here trying to figure out how to get on the air!
I'm in a big apartment building ... I have these hot water pipes which
feed radiators on every floor ... I'm on the 11th floor.

I'm thinking that I can throw 100' wire out the window (to radiate)
and ground to the hot water pipes. Thoughts? Any risk of damage to
the heating system? I don't know how the water's heated...

Thanks,
Rich
(Please don't reply via e-mail ... dead address)