How often you water will depend on whether your plant is potted in bark or a sphagnum moss mix and the amount of light and heat. Paphs need more frequent watering than some other orchids because they have no pseudobulbs to store water. Bark retains less water so will require more frequent watering - every five days is usually sufficient. If your plant is potted in moss, water when the top feels dry. Care should be taken not to overwater to avoid rotting the roots. Soon you will be able to tell by the weight of the pot whether or not it is time to water again. If in doubt, wait a day.