Hope it's all right to revive an older topic, but it is a subject that interests me.
As a fountain pen user for years, I never gave a wink to whether ink was waterproof or otherwise, but more recently as I draw with ink(s) the subject got more of my attention. So for normative writing, I care naught, but for scribbling I cared a great deal. Swipe some watercolour over ink, and you get rather a mess.
I bought a bottle of Document/Archive by De Atramentis recently as it was recommended as "waterproof." Is it? Not quite.
This recent purchase has persuaded to give up the notion that there is a ink that does muster both for both a traditional fountain pen and a calligraphy type pen that might warrant something else.