The supply of water in the right quantity and at the best possible time is an important prerequisite for the growth of the vines and indispensable for photosynthesis. This occurs naturally through rainfall, the amount required (depending on the climate, soil type and grape variety) is generally between 500 and 750 millimetres per year. With ideal soil conditions, however, larger amounts of precipitation can also be tolerated. In the Portuguese Vinho Verde area, for example, the amount of precipitation is 1,500 millimetres. In addition to quantity, the time of year during the annual vegetation cycle also plays an important role.