How to thicken salad dressing I try to maintain a low fat low sodium diet.

I have a homemade salad dressing that I like and is light on oil:  

1/2 cup balsamic vinegar
juice from 1 lemon
1 tablespoon olive oil
1 tablespoon Dijon mustard
2 tablespoons Worcestershire sauce
2 garlic clove
1/2 teaspoon pepper
1/2 cup water  

The only problem is that it is thin and does not stick to the leaves very well.
How can I get better adhesion to the leaves?  

It won't take much more mustard without overpowering the taste.

I don't want to use egg yolk or vegetable as that would limit shelf life. 

I am considering tapioca starch and lecithin oil.
A very small amount of xanthan gum will work.  It is commonly used in salad dressings.  Be careful though, too much will result in an unpleasant texture that some describe as mucus-like.  Maybe start with 1/4 tsp. Wisk in and increase from there as necessary, but in very small amounts.  Xanthan takes a while to hydrate and thicken.  Start with a small amount, as the thickening power will increase with time.  You can always add more later.