Aquaporin channels allow water to rapidly cross cell membranes in all living organisms. AQP1 confers red cells and proximal renal tubules with high water permeability. Present in renal collecting duct, AQP2 is regulated by vasopressin, and human mutants are unable to concentrate urine. AQP0 is expressed in lens fiber cells, and mutations result in childhood cataracts. Brain edema after head injury involves AQP4 in astroglia, and autoantibodies to AQP4 cause episodic blindness and paralysis. AQP5 allows release of sweat, tears, and saliva. Glycerol release by AQP7 in adipocytes and uptake by AQP9 in liver maintains blood glucose levels during starvation. Plants express multiple aquaporins, and full virulence of malaria and other parasites is dependent upon aquaporins. Efforts are now underway to target aquaporins for drug development.