Plants discard the excess water through transpiration, which is the evaporation of it through leaves, stems, and flowers.
Transpiration is regulated by the stomata, which are pores found in the leaves, stems, and other organs.
Conifers have a low rate of transpiration because they have stomata only in the leaves, given that the stem is woody, and their leaves (the needles) have a small surface area; which means there are fewer stomata.