Eventhough it's a small change, you do raise the height of the water level compared to not being there, and thus you also raise the pressure on the bottom and the water will therefore pour out some faster. The pressure that the water pulls of does only depend of the height. James was on to it.
When we're still figuring water out, here's another one for you to find out.
There's a bucket, which is almost filled with water placed on a scales. A person decides to put his finger in the water and does it so that half his finger rests in the water. Will the weight change on the scales or not?