The traditional protocols are fine and don't need any augmentation.
The water would be detrimental because it dilutes the lemon/grapefruit. The minimum concentration of the citric acid content needs to that of a regular grapefruit, about 1.2% by volume.
a. Emulsifies the oil
b. Provides sufficient acidity to bypass any churning delay in the stomach
c. Prevents the secretion of digestive enzymes in the stomach that may inhibit the flush effects when the chyme reaches the duodenum.