Myrtle can apparently interact with water.
There are several cases where she interacts with water:
Myrtle gave a tragic sob, rose up in the air, turned over, and dived headfirst into the toilet, splashing water all over them and vanishing from sight, although from the direction of her muffled sobs, she had come to rest in the U-bend.
Harry Potter and the Chamber of Secrets, chapter 9
"Don't ask me," Myrtle shouted, emerging with a wave of yet more water, which splashed onto the already sopping floor.
Harry Potter and the Chamber of Secrets, chapter 13
So apparently she can interact with water, although no explanation is given why.
Apparently, in the movie adaption, she does touch the taps, whereas in the books it doesn't show anything about the taps, as it directly states that the taps have never worked:
"That tap's never worked," said Myrtle brightly as he tried to turn it.
Harry Potter and the Chamber of Secrets, chapter 16
So the movies shouldn't be taken seriously everywhere (they mess things up).