Student or Learner
1) Turn off the tap ( do we say turn off or something else also what we say to turn it on )
2) Who left the tap running ( I mean the tap was not closed)
And both phrasal verbs are separable, so you can use emsr2d2's versions - 'you turn on and turn off a tap' - or you can turn it/the tap on/off.
But, now I think of it, if you leave it on, that's not separable: 'leave the tap on' but 'leave on the tap' - interesting.