In good health (especially after sickness)

He's been very sick and his wife was really worried, but - thanks God! - he's as right as rain now

È stato molto malato, la moglie era davvero preoccupta ma ora, grazie al cielo, sta bene

I'm no spring chicken but I can't complain: my family loves me, I have money enough to live a decent life and I'm as right as rain

Non sono più un giovanotto ma non mi posso lamentare: ho una famiglia che mi ama, ho di che vivere decentemente e sono in buona salute

“How are you?” “I'm fine, thank you”

“Come stai?” “Sto bene, grazie”

Right as rain follows a long list of curious similes. It was first recorded at the very end of the nineteenth century, although the allusion to rain is unclear. It seems more just a play on words, with a very good alliteration, which made it quite popular