I once had my telephone line fail because of moisture in phone lines along floor in damp basement between studs by some DIY builder.
My thinking is , if your customer specifies that these Type tests must be done, then so be it. Otherwise if cable is compliant, then I would think the test is not needed , but it is designed with materials and process capable of passing.
This might require the cut ends of the jacket to be sealed with Silicone RTV for example, A small amount of water won't cause IR or BDV failure on its own as water is a good insulator but high dielectric constant.
MUddy water on the other hand with minerals is more conductive ( as in my case with light basement flooding) but not called up in the standard as dirty water. Just water. So in my view that means the dielectric constant of 50x for water along the internal jacket may cause sufficient leakage current to cause impedance failure of telephone line and ringer failure as well.
ALthough I have never seen telephone cable siliconed at both cut ends for basement operation, it might be essential for phones to work. ( Remember the days when even when the power failed , at least the phones till operated off CO battery) However it would be nice that the phones would work after the flood water was removed.
None of this is relevent to the question at hand, but puts the problems into perspective. Another example is wiring near boiler tanks and sprinker systems during a fire.