1. Put the olive oil, vinegar, water, shallot, mustard, and salt in a blender. Coarsely chop the basil leaves and immediately put them in the blender.
2. Cover the blender and mix on high-speed for 15 to 30 seconds until the vinaigrette is smooth. If the sauce is too thick for your liking, add a little more water or olive oil to thin it out.