Marie carries around flasks of distilled water for just in case she has to use her abilities while in a humanoid form. She prefers to carry around distilled water because distilled water is the easiest water to control the flow of. Ordinarily the difference in the control-ability of water is so minute that it wouldn’t make a difference but Aquatians aren’t as strong in their humanoid form and notice the tiny difference in control-ability. Marie doesn’t like leaving things to chance and so she always carries distilled water with her.
The idea for water flasks totally came from watching Avatar:TLA. I really liked how practical and useful Katara’s water pouch was in the gaang’s travels and I wanted something equally useful for Marie. However, unlike Katara, Marie is able to use her entire body as a weapon if push comes to shove where as Katara can only use her sweat. There’s also no equivalent to blood bending in the Eternity Complex world. Aquatians control the flow of liquids, a highly skilled Aquatian could drain a person of blood (or other fluids) in a matter of seconds or awkwardly push/pull creatures across the ground but they have no control over the nervous system. What few Aquatians can do to the body of most living organisms is way more akin to what Magneto did to that guard who had been injected with metal in one of the x-men sequels instead of what a bloodbender can do. That scene with Magneto is pretty much the only thing I remember of that x-men movie.