I don't know of any acid anhydride that has completely stability in water, but I think the best way to stabilize them would be to choose a cyclic one, which would therefore favor the anhydride form because it makes a closed ring structure. Looking in that direction, it seems that phthalic anhydride in particular has a rather slow reaction with water (to the point that solubility values are available!).

I don't know of any acid anhydride that has completely stability in water, but I think the best way to stabilize them would be to choose a cyclic one, which would therefore favor the anhydride form because it makes a closed ring structure. Looking in that direction, it seems that phthalic anhydride in particular has a rather slow reaction with water (to the point that solubility values are available!).

Or, if you want a larger ring, homophtalic anhydride (also here):

but I don't find any data on its stability/solubility in water.