Heat up a wok with the oil. When the oil is heated, add the lemongrass, galangal, bird's eye chilies and do a few quick stirs. Add the clams and stir to combine, follow by the coconut water. Add the kaffir lime leaves and cover the wok. Cook the clams for about 2-3 minutes or until all clams are open. Add the fish sauce and lime juice. Stir to blend well, dish out and serve immediately.