Rainwater affects nearly everything it comes in contact with, and it changes its chemical composition based on the compounds that it encounters. These changes are very important to environmental scientists because the chemical qualities of water affect soil conditions and other entities around the world. Rainwater is constantly collected from different geographical areas to test for different qualities.
Rainwater is defined as precipitation that falls from clouds--but usually only rainwater that falls over ground is tested because rain over oceans is often of less concern to scientists. Several different chemical tests are conducted to analyse the qualities of the water, including a hardness test and a pH test.
Water hardness is a test of the mineral particles present in the rainwater. This test shows what compounds are dissolved in the water and usually pinpoints the presence of magnesium, calcium and other elements. This shows not only what effect the rainwater will have on the soil on which it falls, but also from where it came. Most water picks up minerals as if flows through soil and stone; rainwater with a high concentration of dissolved elements also indicates dust in the atmosphere.
pH analysis measures how acidic or alkaline the rainwater is. Absolutely pure water has a pH level of 7, while lower values indicate acidic water and higher values indicate alkaline water. Water can combine with various compounds in the atmosphere to become alkaline or (more often) acidic before it falls as rain. The pH of rainfall is very important and provides a preview of how much it can weather buildings and plants.
The optimal pH level for rainwater for plants tends to be neutral, but this can vary. Certain climates favour plants that need slightly acidic rain, while other soils foster growth that requires alkaline water. If the water is too acidic, the plants will not be able to absorb it properly and will weaken and die.
Rainwater is constantly changing and does not stop changing during its lifetime. When forming in the atmosphere, the water vapour will encounter particles that will change its chemical make-up. When falling to the ground, the rain will encounter smog, dust and other conditions that will affect its pH level. Finally, when rainwater seeps into the soil, the elements in the earth will change it again, and often alter the rainwater's chemistry so that it is more suited for local plant life.