The symbolic meaning (in figure of speech), means that the statement made does not have a sufficient proof to support an argument "Your idea doesn't hold water so we are going to go with plan B"

It's an idiom. When you say that something does or does not 'hold water', it means that the point of view or argument put forward is or is not sound, strong or logical. For e.g., 'Saying we should increase our interest rates because everyone else is doing so will not hold water'.

An argument can be logically complete, leaving no way to get around it. If it is, we can say that it is "tight." If it isn't, we can say "there are holes in that argument." And thus, we can also say "that argument won't hold water." For example, consider this reasoning: a) All dogs have four legs. b) This animal has four legs. c) Therefore, this animal must be a dog. That argument has a hole. The hole is that the animal could be a horse, which also has four legs. That argument doesn't hold water.