Whisk together the egg yolks, vinegar, dry mustard and water using an electric hand-held mixer or a blender. (You have to work hard if you do it by hand.) Add the garlic along with the salt and pepper, and blend again. Slowly pour in the olive oil, mixing constantly to emulsify the eggs and make a mayonnaise-style sauce. If the mixture is too thick, add a little extra water to adjust the consistency.
Stir the chopped herbs in well. Store in the fridge and use within 3 days.