If I were to make a spell using water to ground someone, it would probably involve more the wind element. And would require an ample water supply nearby. A pool, river, fire hydrant, what have you. And would basicly just scoop a large bit of water, and drop itself ontop of the wizard.
basicly would create a water-tight shield around water, move it through the air, and then basicly drop it over the wizard so he would then be within the barrier. not only should this greatly reduce any magical abilities, but you get to drown them too!
Course the barrier would require a great deal of concentration, so the caster would be completely open to attack, and the barrier would only be solid to water, so other physical objects could pass right through it. (leaving gunfire a viable option to the target)