Jar of Water in Piano--Truth or myth?

[Vinny Samarco]

Hi Everyone,
The area of the country I work in is very dry.  Though we talk to many
people about humidity control, most are not interested in what I have to
say.
I recently tuned for a customer who had a very old, but recently rebuilt
upright.
The tuner who did the work is one of the best  that I know of.  Supposedly,
he told this lady to put a jar of water in her piano.
Now tell me, Will that do any good at all, or do you need some form of
distilled water or evaporation in the air to make any difference?
Vinny