Blood is a liquid Enony drinks, as she's a vampire. She, on occasion, drinks her own blood, but suffers no ill consequences whatsoever.
Vrompire drinks it as well. That's how he got his nickname. He is shown attacking and draining a Hufflepuff student.
Apparently, iEbony likes it with Count Chorcula or mixed with beer.
It may be sold in bottled form, as Ebony has some from a bottle early in the story, but it's entirely possible she saved blood from a previous victim and bottled it for later.
In Harry Potter canon, while blood of several different creatures frequently does come up, Harry never develops a taste for it. Hogwarts likewise does not provide it for meals.
In I'm Not Okay, Darren is able to get human blood for Eternity and friends to drink, but only with permission.