The term for the amount of weight that overcomes structural integrity
Solution 1:
First thought was that the water has accumulated to the point of critical load.
Critical defined as:
- Relating to or denoting a point of transition from one state to another.
Solution 2:
Proof load is used in construction and engineering as a term for maximum load.
the greatest load that can be applied to a piece, as a beam, column, etc., without straining the piece beyond the elastic limit.
Maximum load sounds equally good.
Solution 3:
That is the very literal example of the idiom The straw that broke the camel's back.