Plants suck water from the soil by means of negative pressure. So far, it has been an unsolved mystery why the pressure value does not fall below about -100 bar. An interdisciplinary and international research group has now shown, using atomistic simulations and model calculations, that this is apparently due to the so-called lipid aggregates that are contained in the plant sap. The modeling shows that their presence leads to the formation of growing cavities in the water column if the negative pressure is too strong. The limited suction power affects how plants can get water from drying soil.