What Causes PH Levels to Change in Water?

Various industrial processes use water that must be of an exact type of pH reading, and chemicals are then added to change the pH levels. This altered pH in the water is later discharged into sewage treatment plants and bodies of water. Other factors which may change the pH levels in bodies of water are associated with organic material present in the water and plant growth. Decomposed material releases carbon dioxide, which in turn lowers the pH levels in the water.