Get it from an old lady at the top of a block of flats in Celedon City (the one with the grass type gym).
Chat with our AI personalities
you have to find it
In Celadon City you need to go into the Celadon Mansion (Front Door) and talk to the little old lady babysitting the Pokemon she will give you the tea
its simple here goes YOU CAN'T!
In HG/SS you can have tea with her any day from 3:01 - 4 pm :)
Buy fresh water and give it to the guard