Also, the reason water is somewhat deadly to them is all because of the pigment in all their bodily fluids
However, depending on the size of the inkling, A certain amount of water contact with the outer surface of their skin is required to kill them. The pigment contains a hormone-sensitive compound that makes it change color at random. But that compound also reacts with the compound in a different state (like a different color) or water, very dramatically. Thus causing it to foam like baking soda and vinegar. It isn't painful, but its more unpleasant. This forms pressure under the skin, causing them to "splat" or rather die until they respawn.
Also, the reason why the "A player left the battle too early in the match" / "unstable internet connection" error happens, is because one of the teammates player character's ink colors changed unexpectedly.
Also, yes, the pigment is found in EVERY Bodily fluid of EVERY cephalopodic atlantisean and the 2 other fan made species I made.
That includes ink, blood, mucus, vomit, excretements, tears, sweat, etc.