The Total alkalinity (TAlk) of water is a measurement to assess a water sample's ability to neutralize acid. The alkalinity in natural water is mostly caused by weak acid salts, especially HCO3 which is the main form of alkalinity. Other organic acids (e.g. humic acid) which are harder to decompose, would also form salts to increase alkalinity of the water. Weak acid salts such as salts of acetic acid, propionic acid and hydrosulphuric acid would be formed in polluted or anaerobic water. Weak acid salts that are combined with ammonia, hydroxyl ions compose the total alkalinity of a water sample.