ok can someone explain me the meaning of this "witch juice", i understand english but since is not my mother toungue, there are some double meanings like this that i do not get

Beats me. English is my mother tongue and it must be a Japanese thing.

No results in Japanese for "witch juice" either.
I think it should/could have been translated as "Witches' Brew" (=a fearsome mixture.)

Witch Juice is literally the juice from a witch. Its a euphemism for urine. Helma is a pee-fetish character. Its due to the stains on her uniform in her E-wacs profile. That is why another picture on the booru and several others on pixiv depict her peeing her pants.

Snugglemuffins said:
Witch Juice is literally the juice from a witch. Its a euphemism for urine. Helma is a pee-fetish character. Its due to the stains on her uniform in her E-wacs profile. That is why another picture on the booru and several others on pixiv depict her peeing her pants.

asuming the bottle contains her own urine or other witche's urine...

and given what you said...

and her facial expresion...

WAIT! is she thinking about drinking it?!