Is there enough water in the oceans, ice caps, rivers and streams to cover a completely flattened earth, in proportional to land volume and water volume?
Here is a very simplistic approximation: The total volume of the oceans (no lakes, rivers, water vapor) is around $1.3\ 10^9$ cubic kilometers. The surface area of Earth is around $5\ 10^8$ square kilometers. Dividing the volume by the area, we get a depth of 2.5 kilometers. The fresh water contribution is about 3% of the volume of salt water.
In reality, other factors such as the fact that Earth is not spherical, density changes, and that the water will be acted upon by tidal forces and other interactions, will make the distribution uneven.