Interesting one. Rainwater should be free of calcium and lime deposits which come from groundwater. There are contaminants in the atmosphere which rain dissolves as it falls through them (industrial pollution in the cities).
That should not be an issue in the clean country air.
Do you need to de-scale? If you have an electric jug which has been fed rain water only, look at the bottom of it and the element. If you see a rusty deposit, the answer is yes, you do have to descale.
But it would seem to be unlikely.