Hydrochloric acid (HCl)
Can be used in water treatment to lower the pH of the water, making it more acidic. This can be useful in removing heavy metals and other dissolved impurities from the water. Additionally, it can help to control the growth of microorganisms, such as bacteria and algae, that can cause problems in water distribution systems. However, the use of hydrochloric acid in water treatment must be carefully controlled to prevent the acidity from becoming too high, which can lead to the corrosion of pipes and equipment and can also be harmful to aquatic life.