The Angel Wing Begonia is a thirsty plant that will need watering as often as every day during summer. It likes to be kept in continuously moist but not soggy soil, so you should aim to keep the top layer of soil moist to the touch without overwatering the plant.
Although it likes to be watered frequently, it can suffer from root rot if overwatered, and this will be fatal for the plant. Always remove water that has drained out of the pot and do not let the plant sit in excess water.
During winter, you can reduce the frequency of watering, but the plant still likes its soil to be kept moister than most. Aim to keep the lower layers of soil lightly moist, allowing the top layer of soil to dry out before watering the plant again. Never allow the plant to dry out completely. Always water the plant at soil level to prevent the leaves from getting wet, as damp leaves can cause fungal diseases.