Oysters, like all bivalves, constantly cycle sea water through their system, which causes sand to enter the oyster. According to Astray Recipes, "Oysters ingest about 100 gallons of water a day in order to filter out the one-celled organisms that are their food." In this process, sand enters the system, the majority of which is removed naturally. An annoying part of consuming oysters, the remaining sand may be eliminated by soaking and cleaning the oysters immediately before consumption. This should only be done immediately before eating the oyster, as the fresh water will dilute the flavor and eventually kill the oyster.
Run cold water in a sink. Gently scrub the oyster shells with a small scrub brush to get the sand off the shells. Place the scrubbed oysters in a large bowl filled with one gallon of fresh water and one-third cup of salt.
Soak the oysters for 20 minutes. The oysters will cycle the water through their system, cleaning themselves, and expel the sand.
Repeat this process two more times, being sure to use clean water for each soaking.
Remove the oysters from the bowl, empty the water and rinse before shucking, serving or cooking.
Oysters may be refrigerated for up to a week, either in their shell or their natural liquor. Do not store the oysters in water, which will eventually kill them.