Finely grate or chop the cucumber. Finely chop the garlic cloves. In a large bowl, mix the plain yoghurt, sour cream, chopped garlic, olive oil, and water. Add a pinch of salt and some pepper. Add the grated or chopped cucumber and mix thoroughly. Garnish with a little extra pepper and refrigerate. Serve with sliced baguette bread. Goes well with gyros or ribs.