To remove water from a mixture of sand and water, the appropriate method to use is:
Filtration
Filtration allows the solid sand particles to be separated from the liquid water, as the sand will not pass through the filter while the water will.
Centrifugation might also work in some cases, but it's not the primary method typically used for separating sand from water. Magnetism is not applicable here since sand is not magnetic, and floatation is not relevant for separating these specific materials.