Basic requirements for paper to practice aquarelle
When it comes to watercolor, the one place I really recommend avoiding going student grade on is the paper. There are some really excellent student paints, but for paper, meh...

On that front, the biggest names in paper are Arches and Fabriano, but what you're really looking for is 100% cotton rag at 140 lbs in any brand. Some are, really, better than others, but it gets a bit more marginal in the higher end. The key, though, is that is 100% cotton.

So, why? Well, the behavior of the paper is important. Lower quality paper is usually more absorbent, has less sizing, and is much more likely to buckle and warp. In other words, the behavior of the water and paint on the surface is going to be very different when compared to professional grade alternatives. Given that watercolor is already a challenging medium, why make it even harder? Practice on the best you can afford, especially if you want the same techniques to apply to the final copy.