Water is not compressible While gases can be compressed into smaller and smaller spaces, liquid water is not so compressible. Thus compression of water into a space surrounded by a cell wall produces turgor pressure . Turgor keeps petals and leaves extended into the air and prevents wilting. M Pa typical tire pressure is 0.25 MPa. Water is commonly available Because of the water cycle, rainfall and ground water are linked through the transpiration and evaporation from plants.
Water is a free medium for cell and body enlargement.
Of course foolish humans douse this effect by piling ladles full of salad dressing on their vegetables. While water is often commonly available, water can be insufficient during important times in the life of a plant. A drought is common in late summer and can reduce the yield of crop plants quite significantly. Because plants need water for photosynthesis, for evaporative cooling, and a host of other uses they can run through a staggering amount of water. This all has to be replaced from the soil at these rates to keep up with the water demand.