Distribution of sodium and potassium ions :
Sodium and potassium are chemical elements commonly found in soils and rocks. They belong to a group of chemicals called the "alkali earth metals." They are often associated with chloride and bromide. They are released slowly upon dissolution of rocks. Consequently, their concentrations increase as residence time in groundwater. Sodium occurs in freshwater because of exchange of dissolved calcium and magnesium for sodium in the aquifer material. Sodium and potassium are important ions in groundwater and are used to assess quality control for samples and laboratory analysis. Both Sodium and potassium are often useful for identifying the source of groundwater. Sodium has some utility as a tracer of human and animal waste in shallow groundwater. Sodium in large concentrations (>170 mg/1), may affect persons with cardiac difficulties, hypertension, and certain other medical conditions. Depending on the concentrations of calcium and magnesium present in the water, sodium may be detrimental to certain irrigation crops (Palmer, M. 1996). Potassium is an essential nutritional element, but in excessive quantities, it acts as a laxative, and 12 mg/L is regarded as the extreme limit of potassium permissible in drinking water.