Is gillyweed in gillywater?

[Fred Waldrop <fredwaldrop@yahoo.com>]

No: HPFGUIDX 51827

I have looked in Harry Potter Lexiton, even E-mailed the Editor to 
find out, but alas, no luck yet. So, I came here, to where there are 
thousands of people with better minds than mine.
My question is :Is gillyweed in gillywater?
The reason I ask this, in Harry Potter PoA, Professor McGonagall 
receives a drink she ordered (Chapter 10,page 202, USA edition), it 
was "gillywater".
But, in Harry Potter GoF, Harry used "gillyweed" to transform himself 
to be able to breath under water for the 2nd task,(he got gills after 
eating the gillyweed,[chapter 26, page 494, USA edition]), and if 
gillywater has gillyweed in it, why did it not transform Professor 
McGonigall?


Fred Waldrop