Heat oven to 325°F. Place ham, fat side up, in foil-lined roasting pan or on rack in shallow roasting pan. Pour water into pan. Bake at 325°F. for 1 hour.
Remove ham from oven. Add sherry to roasting pan. If necessary, trim fat from ham. Score ham diagonally at 1-inch intervals, cutting about 1/4 inch deep; score in opposite direction to form diamond shapes. Insert meat thermometer so bulb reaches center of thickest part of ham, but does not rest in fat or on bone.
In small bowl, combine marmalade and mustards; mix well. Brush half of marmalade mixture over ham. Spoon pan juices over ham.
Return to oven; bake 1 to 1 1/2 hours or until meat thermometer registers 140°F., spooning pan juices frequently over ham and brushing with remaining marmalade mixture.
Let ham stand in roasting pan for 15 minutes before slicing, spooning pan juices frequently over ham.