I was always told NEVER to use the hot water pipe, it can be dangerous. A
cold water pipe could be fine.
Using the house ground can sometimes work, I have seen hams use the "tube"
that brings the wires from the roof to the box with great success. Other times
using the house ground causes what is known as a ground loop and you can get
all kinds of noises.
A good ground is usually a 6' or longer copper ground rod or copper tubing
into the ground and just attach the ground wire to that. Just make sure you
know what is under the ground before you start pounding a ground rod into it.
The shorter the distance from the radio to the ground rod the better.
As for getting that 6' rod into the ground, that isnt always easy depending
on your soil. A root feeder can be of help. It will really get the ground rod
started in easily and soak the earth underneath as well.
I have also seen several ground rods used. Just attach a heave copper wire
to each ground rod and then the main one to the radio. This gives more ground
coverage.
Craig N0BSA