500 g plain yogurt
1 cup (240 ml) water
1–2 cucumbers, diced (diced is far better than grated, although at many restaurants they grate them)
A couple of spoonfuls chopped dill
Salt, to taste
Vinegar, to taste
Oil, to taste
A couple of spoonfuls chopped walnuts (optional)
Mix all the ingredients, using enough water so the soup is about the consistency of milk
Serve cold in a soup dish, adding a couple ice cubes if it's not cold.