During an ice age much of it becomes "trapped" in glaciation and the global climate and humanity might then suffer a shortage of available water. We are no doubt headed in that direction, although whether it will happen in the 21st or 22nd centuries, or tens of thousands of years out isn't yet clear. But when it does I somehow think we will be able to cope.
Pollution is of course a separate problem but can be solved (and has been largely solved in the "evil white European descendant" countries) through reasonable environmental regulation and investment in technology, including desalination from sea water.
He will have to forgive me. I am cursed with a 1960's middle and high school science education plus some college courses in geology. My education must lack the heavy gravitas of a journalism degree.
We are drawing down the aquifers. The water isn’t disappearing though.
People used to be able to hand dig wells in my area as little as 90 years ago. Springs that used to run reliably in the past are dry year round. The average well depth currently seems to range from 500 - 600 feet.
The water’s there, it just takes much more effort to get it.