Blend together water, tomatoes, cucumber, leek, and celery until you get a juice.
In a bowl, filter the juice with a fine strainer. Add condense pistou and salt (see recipe below). Mixwell with a whip.
When serving, mix avocado and watercress. Add the vegetable blend to the stock and stir.
Condensed pistou.
Grind all ingredients in a blender until a uniform paste is obtained.
Notes
To prepare the stock, dilute 1 1/2 tbs of this mixture into a cup of water.The condensed pistou will keep a month in the fridge in a sealed container.The soup will keep for 2 days in the refrigerator in an airtight container.