[bayindirh]

Water based inks come in tons of flavors. You can have washables (most of your royal blues), "permanents" (most blue blacks and special formulations) which leave a faint mark you can't remove (GvFC inks sans Royal Blue, Pelikan 4001 Blue Black, etc.), pigments which cling to your paper like their life depend on it or you can go full send and get "cellulose reactive" inks which will not leave your paper unless you destruct the said paper.

Many "permanent" inks on permanent rollerballs and gels (e.g. Uni SuperInk) is also water based, yet they don't and won't leave your paper, because they're made of UV resistant pigments.

[ykonstant]

Right, or you can use an oil based ink with a good ball point pen and not have to worry about where to find "cellulose reactive" inks and how they will interact with your fountain pen.

[bayindirh]

Noodler's inks are dime a gallon, esp. in the US, and they're guaranteed to be pH neutral in most used colors (bottles state if they pH neutral), so they don't damage any pen, modern and vintage.

They're specifically designed to be that.

Bulletproof Noodler's inks are as follows: https://noodlersink.com/product-tag/bullet-proof/

They even have 16 Oz. bottles if you want "buy one, leave for grandchildren" amount of ink in one go.

If you want a more mainstream archival ink, go GvFC, Pelikan 4001 Blue Black (not available in US), MB midnight blue or Pelikan Edelstein Tanzanite.