Sand is available in many forms for purchase. If you want pure white sand you will need to get it from a beach that creates white sand, such as Destin, Florida, or from a craft store. Pure white sand is chemically dyed. Natural sand gets it pigment from the things it is made up of. Different varieties of dirt, shells, gravel and organic material colour the sand. If you have particularly dingy or brown sand, you can lighten it by bleaching it in the sun. It may not get pure white, but the sun will lighten it considerably.
Spread the sand in shallow trays, such as baking trays or plastic tubs, so that it's one-half-inch thick. It needs to be thin for the sun to penetrate all the grains.
Place the trays in a sunny spot where the sand will be protected from moisture. Don't put it outside until there are a few sunny days in the forecast.
Bleach the sand in the sunlight for two to three days. Stir it around with your hand and spread it back out once a day.
Leave it out longer to lighten it more. It will not lighten to a bright white no matter how long it sits in the sun.
The sun will also sanitise sandbox sand. The same bleaching power that lightens it will kill germs as well.