Drop a couple objects into the water to show students how you would like them to place the objects, avoiding splashing, and showing them what you are looking for to determine whether the object floats or sinks.
Make a "float" and a "sink" pile and put your objects in their corresponding pile.
Split your class into groups, one for each work station.
Have students test one object at a time, placing them into their own "float" and
"sink" piles as they finish.
As groups finish, go around and check their "sink" and "float" piles for
correctness.
Ask students to clean up any spills that may have happened, then to return to
their seats.