Hydrogels

I worked with Hydrogels many years ago. I don't think I have ever come across a specific practical or method to extract water from Hydrogels. Exactly how Hydrogels work is still abit of a mystery among the science community. 
The student would need to use their own scientific experience to design a suitable method. The Hydrogel is a polymer and depending on which one you buy will decide just how much water the polymer holds. I am aware of three ways to remove water from the Polymer. Briefly one involves using salt. Adding the salt in the water will decrease the total water absorbed by the hydrogel and the hydrogel will shrink, giving up some of its water. The second involves loweing the pH. That's a longer chemistry explanation. Both methods will require further study by the student.
In any case, as my preferred third alternative, I would suggest that the student borrow the principals of Silica gel. In an oven set at low temperature heat (put your sample at about 30-40 deg C in an Oven) the hydogel until its mass does not further change. In effect you are driving off the water and leaving the polymer. From this point foward I would suggest that adding fixed amounts of water and weighing the polymer until there is no further increase in mass. You would have to work out a way of making sure that the water added was actually stored by the polymer and not elsewhere!
Some hydrogels can absorb as much as 600 times their original volume of water. They will absorb more purified water as it contains fewer ions