In a large saucepan, bring the water to the boil over high heat.
Add the salt and the French beans to the pan.
Reduce the heat to moderately low and simmer the beans for 5 to 15 minutes, or until they are just tender.
Remove the pan from the heat and drain the beans in a large colander.
Set aside.
In a large frying pan, heat the oil over moderate heat.
When the oil is hot, add the onions to the pan.
Fry them, stirring occasionally, for 5 to 7 minutes, or until they are soft and translucent but not brown.
Remove the pan from the heat.
With a wooden spoon, stir the paprika, tomato puree and sour cream into the onion mixture.
Return the pan to low heat and mix in the drained beans.
Cook, stirring occasionally, for 5 minutes or until the beans and sauce are heated through.
Remove the pan from the heat and turn the mixture into a large, warmed serving dish.