Yes, geraniums can be rooted in water. Take cuttings about 6 inches long and remove all but the top leaves. Put the cuttings in a jar of water in a bright spot but not in direct sun. Be sure to remove all foliage from the cuttings that might fall below the water level; leaves in the water will rot. With luck, the cuttings will send out roots eventually and can be replanted.
You may have greater success by rooting the cuttings in moist vermiculite or perlite. These soilless products promote excellent aeration as well as holding in moisture. Dip the lower end of the stems in rooting hormone to enhance root development. Geraniums do well with a slow-release granular fertilizer designed for annual flowers.