Obviously a hydromancer could do a Dispel type spell and have an easy excuse for it, just as a spirit caster can easily justify an invisibility+avoidance type veil of the sort Molly uses.
You don't get it for free as a side-effect of other magic though. It's something you choose to do, just like hexing or whatever. You can use water as a ram or water to make someone choke or water to dissolve things or water to dispel by grounding out, just as you can use fire to attack, or to set somebody on fire, or to vaporize a barrier or to "cleanse" some types of magic by burning.
It's just flavor for an effect. Most elements can do most things, water does dispels by "running water" over the effect and "grounding it out".