This question is not very clear, and more information is needed to give an accurate answer. The following are possible explanations:
1. If it refers to an actual water wall, you need to know the length and width of the water wall, as well as the shape and height distribution of the water wall. Only this information can calculate the average height of the water wall or the height of the highest point.
2. If it refers to a fictitious water wall, it is necessary to know the specific description or image of the water wall so as to estimate the height of the water wall according to the description or image.
3. If it refers to an analogy, for example, something is like a water wall more than two feet high, then it is just a metaphor, and the height of the water wall does not need to be calculated.