Heat the oil in a very big pot, over medium heat. Add everything except the water and the pepper and turn down the heat to a low heat; it should just simmer, but not change colour. Saute for 30 minutes at least by low heat. Add water and turn up the heat. Bring to boil and let it simmer for 15-25 minutes. Pour it into a blender and blend it. Pour it back into the pot, while pressing it though a sieve. Bring to boil again and add black pepper to taste.

I just finished making this soup and it's very nice IMO. The amounts given in the recipe are very un-precise, but try to work it out for yourself.