Is mixing sodium chloride sand and water a chemical or physical change?

It depends on how the mixing is performed. If you take the two solids and mix them then it is a physical change as you get a heterogeneous mixture of solids. If you dissolve and them and mix the solutions- then a chemical change may occur- as different compounds are formed.

Na2CO3 + CaCl2---> 2NaCl + CaCO3