Most waters contain some Chloride. It can be caused by the leaching of marine sedimentary deposits and by pollution from sea water, brine or industrial and domestic wastes. Chloride concentrations in excess of about 250 mg/l usually produce a noticeable taste in drinking water. An increase in chloride content may indicate possible pollution from sewage sources, particularly if the normal chloride content is known to be low. Where only waters of very high natural chloride content are available, reverse osmosis or electrodialysis units may be used to produce potable water.