Plants are autotrophs or obtain all the nutrients they need from the environment around them. Rainwater plays an important role is this function. Rainwater is the most natural way for plants to obtain moisture. Tap water often has added chemicals as it's treated and recycled for human consumption. Rainwater has a higher level of oxygen and is free from harmful minerals and additives found in tap water, according to Texas A&M University.
Water makes up 80 to 95 of herbaceous plant tissue and 50 percent of woody plant tissue, according to Clemson University. This water is lost through transpiration, a form of evaporation, throughout the day and must be replenished. Several factors, such as heat, the sun and type of plant, determines the transpiration rate and the amount of water each plant needs. Plants use the moisture in the soil to replenish the water lost through transpiration. If there is no water in the soil, the leaves will wilt. As more water is lost, the plant will fail and eventually die. Rainwater builds up the moisture levels in the soil and assures a healthy plant.
Rainwater frees nutrients and minerals in the soil the plant needs to survive. As the soil absorbs rainwater, a film forms around soil particles, according to Bellevue College. Roots then absorb these particles in a process called diffusion. These nutrients are carried to the rest of the plant. Lack of water leads to mineral deficiencies and an unhealthy plant. In addition, the plant uses water alongside photosynthesis to make sugar. Water carries this sugar through the plant by water to feed individual plant cells. The cells then convert the sugar into energy, which the plant uses to produce leaves, flowers and fruit.
Acid rain is common after volcanic eruptions or when excessive amounts of sulfur dioxide or nitrogen oxides are released into the air from fossil fuel combustion, according to the U.S. Environmental Protection Agency. These gases merge with water and oxygen in the atmosphere to form an acidic compound. When this compound falls in the form of rainwater, the soil absorbs it. The acidic nature of this rainwater dissolves and removes the nutrients in the soil and increases minerals that are harmful to plants. Frequent exposure to acid rain kills plants.