The pH level is the amount of acidity that the water has. The pH level is important for plants because they have a difficult time taking up nutrients from soil that is too acidic or not acidic enough, according to the University of Vermont. Water that is acidic seeps into the soil and increases the acidity of the soil, which can be detrimental to some species of plants and can be helpful for other species such as blueberry bushes. When water contains a low pH level, the pH can be raised by adding lime to the soil.
Water becomes acidic when industrial chemicals are mixed into the water. Water can also become acidic when chemicals are used to lower the pH of soils that are too alkaline and seep into the groundwater, causing the groundwater to become too acidic, according to the University of Georgia. Acidic gases that are released by industrial processes can mix with water vapor and produce acid rain that can become a part of the water cycle.
Plants prefer water that has a neutral pH of 7, which is the case with pure water. The acidic water can lower the soil pH and make it more difficult for the plant to take up nutrients in the soil and the acid can also become corrosive to the plant when present in strong enough concentrations.
Acidic rain can have a positive effect on plants. The acid breaks apart compounds that release nutrients that the plant must absorb, according to Cactus and Succulent Journal. The acid also creates an environment that is beneficial to bacteria that engage in nitrogen fixation and produce nitrates that can be absorbed by the plants nearby.
Bacteria prefer only slightly acidic soil. More acidic soil can dissolve and destroy the microorganisms. Soil that has a pH level below 5–usually because of acid rain-breaks down aluminum hydroxide. The released aluminum interferes with a plant’s ability to absorb calcium and also reduces the number of bacteria in the soil, according to Elmhurst University.
Some plants change the colors of their flowers when they take up acidic water. Hydrangeas have flowers that turn blue when they take up acidic water. Many gardeners attempt to change the color of their hydrangeas by adding acidic water, but the water sometimes seeps into areas away from the hydrangeas. This can be prevented by growing hydrangeas in containers so that the acidic water remains in an area that can be taken up by the hydrangeas. This technique will not work on white hydrangeas at all.