A leaf really does have the water and sewer system going on through the veins you can see. They do double duty though unlike a man made city where you'd better separate them or face a major disaster.
Even the drainage, or rainwater, that hits the leaves will travel down these paths and end up flowing off of the point of the leaf. Trees that are more adapt to a rainforest environment even have a more pointed tip to the leaves to assist the water as it pulls together toward the tip and falls off of the leaf to minimize the weight, and thus potential damage, on the branches.
Pine needles are really good at this. The pointy long leaves barely hold any water at all, dripping like nobody's business. We used to camp a lot and the piny woods of East Texas was a favorite. The smell of a pine forest after a summer rain is something you don't soon forget.
A good leaf picture also makes a good desktop wallpaper. Not sure if this works real well since it's only taken with my iPhone, but it could be worse.
