The frequency with which you water a lily plant depends on several factors, including the type of lily, the climate and weather conditions, the potting mix, and the size of the pot. As a general rule of thumb, most lily plants need to be watered once a week. However, during hot weather or when the plant is growing rapidly, you may need to water more often. When in doubt, it's always better to err on the side of too much water than too little. Too little water can cause the lily plant to wilt and even die.