Water
"Shortage" may not be the right descriptor. Plenty of fresh water exists world-wide, but the sources are not where wanted, not easy to tap, or polluted. Rivers, the major source of human water, are well tapped. Six major ones are nearly tapped out (Source, Gleick).
The rivers "tapped out" or nearly so: Colorado, Amu Darya, Nile, Fen, Ganges, Indus, and Yellow. Tapped out means that much of the year these rivers are nearly dry at the mouth, so prior silt accumulations in their deltas no longer replenish soil, for instance. In addition, many lesser rivers have to be very carefully managed. The Rio Grande is one.