MONSOON RAINWATER CHEMISTRY AND ITS POTABLE STATUS: A CASE STUDY FROM SOUTH-EAST COASTAL BELT OF BANGLADESH

Abstract

Major ion chemistry of rain water from a selected area has been determined. The rainwater is slightly acidic as in the case with rain waters globally. All major cations and anions are present in delectable amount. HCO3- is the dominant anion in the study area and its concentration generally decreases subsequent showers. Such decrease in concentration also is noticed in case of other cations and anions. The influence of seawater in the chemistry of rain water is quite significant in the present study. Although at the beginning of the first rainfall event, bicarbonate ion predominates, its concentration gradually diminishes with the passage of time, but sometimes erratic values are noticed and even in the last fraction of a continuous rainfall. Most of the other cations and anions behave similarly to that of bicarbonate ion. Concentrations of various chemical constituents are not constant in local rainwater and it varies from rainfall event to event. It is also dependent on the various local meteorological parameters. Different calculated weight ratios such as SO42-/Na+ etc. are compared with seawater. The results indicate the influence of southern seawater to a great extent. Moreover, non-marine origin from the onshore such as dust particles, automobile exhaust, smoke etc. also contribute significant amount of the dissolved constituents in the rainwater. A household survey was conducted to know about the water using pattern of the study area. However the calculated major cations and anions are below the potability status of DoE standard which is not viable for human health.