The meaning of "does not hold water" is:
The definition of "does not hold water" is:
(idiom) a statement does not appear to be correct or reasonable
A: I believe that dinosaurs were on the earth 6000 years ago.
B: That theory doesn’t hold water. The earth isn’t that young!
When she told me that she thought the sun revolved around the earth, I told her that it doesn’t hold water. The earth moves around the sun!