Incorrect: There is a leaking on a pipe. Correct: There is leaking from a pipe. OR There is a leak from a pipe. Also correct: Water is leaking from a pipe. We don't use 'a" with "leaking" but we would use "a" when we state that there is A LEAK Also, You can say "ON a pipe" but it is not normally said...usually we would say leaking FROM a pipe. Okay? :)

The noun form is "leak" - there is a leak in this pipe! The pipe is leaking ! (verb) It's a leaky pipe! (adjective)