OK.
I GET it. But the only time I’ve drunk/drank/drinked rainwater is when I’ve been out in the pouring rain and opened my gob (?Rewind!)
But I DO KNOW from 1st hand experience that it’s the best water to wash your hair with.
As a youngster, living with Nan and Grandad we’d do the hairwash ritual.
Every saucepan in the house taken into the garden to scoop out the rainwater from the tubs/barrels. Bring them in and put them on the stove.
About 1/2/3 hours later we’d have enough warm water to wash my hair in the kitchen sink.
God’s Honest!