There may or may not be a drain right at the bottom, but you can make it so.
Cut a hole in the outer casing about 250 mm across. Dig out the insulation material and you may see a bolted on cap. Really depends on the make/model of HWS you have.
If there is a cap remove it drill a hole and weld on an elbow. If there isn't a cap you can still do the same.
Just sit the unit up on 3 bricks or something to raise it up off the floor to allow room got the pipework to run out underneath.