Please solve the programming task below using a self-contained code snippet in a markdown code block.

Given an n x n grid containing only values 0 and 1, where 0 represents water and 1 represents land, find a water cell such that its distance to the nearest land cell is maximized, and return the distance. If no land or water exists in the grid, return -1.
The distance used in this problem is the Manhattan distance: the distance between two cells (x0, y0) and (x1, y1) is |x0 - x1| + |y0 - y1|.
 
Please complete the following python code precisely:
```python
class Solution:
    def maxDistance(self, grid: List[List[int]]) -> int:
```