Combine the marinade ingredients into a gallon-sized, re-sealable plastic storage bag. Seal and shake vigorously to combine. Add the shrimp and marinate in refrigerator for 2 - 3 hours.
AWhile the shrimp is marinating, pour the water into a shallow bowl. Juice the lemon and add to the water. Coarsely chop the lemon and add to the water. Put the skewers into the shallow bowl so they lay flat and are completely submerged; this will prevent the skewers from burning during the grilling process and will impart a little lemon flavor to the shrimp.
Thread the shrimp onto the skewers so the shrimp lay flat - first through the head and then through the tail. Add a tomato and grape and then another shrimp. Put 3 - 4 shrimp per skewer with tomato and grapes between each shrimp.
Grill the shrimp on medium-high heat outside on a grill or inside on a preheated stainless steel grill pan. Grill the shrimp for 2 - 3 minutes per side or until the shrimp turns pink and has developed some grill marks. Salt and pepper to taste.