I drew the squares in pencil, draw a line on the left on dry paper and touched the line with water to make it bleed. I then did a second line on the then-wet paper to see how it dispersed in wet. Then I did the cross-hatching on the right of the square on dry paper, then painted the rectangles and allowed all of them to dry completely. I then painted a wash of water through the square and some immediately re-wet, others were completely waterproof.
For writing you may not need to use waterproof ink, and even for drawing you may prefer to have water soluble ink if you wish to use water to create some tones. I just like to know what my materials will do.
The Calli inks were also completely waterproof.
I am using Da Atramentis Document inks in Black and Brown in my fountain pens and am very happy with them. I'll also use their regular non waterproof inks for writing and some drawing, and Lamy inks in my Lamy pens. The rest I prefer to use with a dip pen in the studio.