Yes, this sand can be put in water, but I have had sand cause problems for my filters (impeller jams), and it has the potential to cause irritation to the eyes, nose etc. if your turtle digs through it. If your turtle is eating gravel, try using larger stones, such as river pebbles, which are too large for your turtle to eat. They can be used by themselves, or as a layer over the smaller gravel, to keep your turtle from eating the smaller gravel pieces.
If you are going to use sand, I would recommend putting it in a bucket first, and rinsing it until the water runs clear. Most sand contains a lot of dust, which is natural, and fairly harmless, but will make your water look muddy and unclear.