u/Atoman666

My wife and I have noticed this white residue appearing under our bathroom window. Unsure of the exact timing, but it's some time in the past year that this has appeared. There are no pipes going through this section of wall as far as we are aware, but our internal window sill does pool with water from the shower.

Its not in a position where I can easily brush it, but it seems like efflourescence to me. House is a 1930s build, and no other windows or bits of wall seem to be affected.

I was wondering if someone with a bit more knowledge could let me know what might be going on, and how worried about it I ought to be? Is this just an aesthetic issue, or could we have some serious water damage?