"There was something that I forgot to do!"
I hesitated to use this picture from the Muppet Wiki because it gives away the ending, but then I realized that you can hear the water running from the beginning of the sketch, so the ending is really never a surprise anyway, so long as you're paying attention. As a matter of fact, it surprises me that Bert doesn't notice the water running. It seems to me that he would walk in and say, "Ernie! You left the water running in the bathtub!"
My favorite part of the sketch is Ernie's little "help!" at the end.
Why is there a coatrack in the bathroom? I imagine it's probably supposed to be for towels. It doesn't help that they apparently just redressed the living room set to look like a bathroom. I guess they thought no one would notice. I never noticed until just this minute.