Most of you are too young to remember, but the leading advocate of urine-drinking in my lifetime was former Indian Prime Minister Moraji Desai, who was in office in the 1970s. It was much written about in that time.
As Wikipedia states, “In 1978, Prime Minister Morarji Desai, a longtime practitioner of “urine therapy”, spoke to Dan Rather on 60 Minutes about the benefits of drinking urine. Desai stated that drinking urine was the perfect medical solution for the millions of Indians who cannot afford medical treatment.”
You don’t say when Salinger started this habit/treatment/self-drinking, but I suspect it was about that time, when urine-drinking became a fairly fashionable meme.