Well, according to a study from the University of Utrecht, they're the four countries most imperiled from groundwater depletion. Oh yeah, and they all have nuclear arsenals.
Three of them are facing a freshwater crisis, have nuclear arsenals, and vie for the same Himalayan headwaters. That, of course, would be India, China and Pakistan. To complicate matters, those three have various disputes about the others' claims to those headwaters. From The Montreal Gazette: