Thanks for all the replies. I guess I should clarify a few things.

Reduction in house value - Several realtors I've spoken with say an
average-sized pool adds only about $10,000 to the value of the house, even
though installation of a pool can run $25,000 or more. The person who may
potentially lose money on a pool is the house owner who has one installed
and then thinks he will get all his money back. As was pointed out by Ann,
a pool can be perceived to be a liability and a white elephant - and that's
exactly how I perceive it. I would be offering less for a house with a
pool, so I would not be "losing money".

Plumbing and drain issues - duly noted, thanks, although I believe pools
have recirculating pumps and are not hooked up to the house plumbing. The
inlets would have to be plugged with concrete or something.

Permit issues - duly noted, even though I am looking at houses in the
country, this is something to be aware of.

Water garden or Fish pond conversion - thanks for the links, they are very
pretty ponds, but I'm interested in vegetable gardening.

Soluble concrete salts - thanks, good idea, I will look into this.

Insurance liability due to busted up bottom - thanks, I will ask my
insurance company about this.

As another plus, some of these houses have little gazebos or pool houses
that would be just perfect for a nice gardening shed and potting bench :-)

Dee