Not trying to be a smart ass here, but why are you certain this could not be hard water deposits? That was actually my very first thought looking at the photo, as I also have hard water, and sometimes see this with calcium on strawberry leaves, and on dried dishes after hand-washing them and leaving them to air dry. If it's mildew, spider mites, or something similar, you can try methods such as spray on neem oil, or a diluted hydrogen peroxide solution to eradicate the disease without harming to plant. Best of luck whatever the case may be for you.

[–] Rutty@sh.itjust.works 1 points 6 months ago

I’m not, I just am surprised that deposits would develop after watering. I really shouldn’t be though.

I’ll keep an eye out and see how it develops. Thanks for the input.

[–] catloaf@lemm.ee 1 points 6 months ago

Are these indoor, outdoor? Do they wipe off?