Kent Hovind already proposed the perfect creationist model for this. It was the same amount of water as we have today. The difference is the Earth back then was more flat and soils more evenly spread out.
If you think about it, the bible never stated that the entire earth was flooded all at the same time. Therefore, it must have flooded one region at a time until the entire earth was covered. I propose (in creationist terms) that massive tsunamis were responsible and that every part of the earth was covered at some point.
Not necessarily. Remember that the topic is where did the water come from and where did it go? Same amount of water. Just rearranged landscape. Right before the flood, god could have rearranged the earth's geology and voila floods!