I’ve been reading how it’s good to write certain Surahs, dissolve it in water (I’m guessing) and then drink it – different surahs have different effects.
But I’m wondering what do we actually use to write the surah? And is dissolving it just a matter of submerging the piece of paper into a container of water?

Sometimes saffron is used. So get a wooden pencil, then dip it in saffron water, then write it in a plate, and then drink the water in that plate.