In my first junior high science class, my teacher asked us all that question. he played devil's advocate trying to convince us that it was leaking through the bottle. so we said "why does water, not juice, appear on a container that's filled with juice?", he responded by saying that only the water can pass through the container. Looking back on this, he was getting at a pretty good thing there. he made us explain something that we all intuitively knew (condensation) in a scientific way, rather than just by intuition.