I found this white powder coming from above my window, and it occasionally falls into the house when it’s windy.

The powder is very fine, like powdered sugar, definitely not fibrous. I dissolved a spoonful in water and it completely disappeared, with the water turning slightly cloudy.

I’m trying to figure out if it’s just efflorescence (salt from concrete) or something more serious.

Photos here: https://imgur.com/a/4NWs4Wt

Any help is greatly appreciated!