Source of Carbon DioxideFree carbon dioxide (C02) exists in varying amounts in most natural water supplies. Most well waters will contain less than 50 ppm. Carbon Dioxide in water yields an acidic condition. Water (H2O) plus carbon dioxide (C02) yields carbonic acid (H2C03). The dissociation of carbonic acid yields hydrogen (H) and bicarbonate alkalinity (HCO3). The pH value will drop as the concentration of carbon dioxide increases, and conversely1will increase as the bicarbonate alkalinity content increases.
H20 + CO2 <===> H2CO3 <==> H+ + HCO3
Water with a pH of 3.5 or below generally, contains mineral acids such as sulfuric or hydrochloric acid. Carbon Dioxide can exist in waters with pH values from 3.6 to 8.4, but will never be present in waters having a pH of 8.5 or above. The pH value is not a measurement of the amount of carbon dioxide in the water, but rather the relationship of carbon dioxide and bicarbonate alkalinity.