A preservation study was carried out to determine the stability of inorganic species of arsenic as arsenic(III) and arsenic(V) in distilled and natural waters for a duration of 125 d. Various conditions of storage, such as pH, level of arsenic, type of container material and size of container, were studied. It was found that arsenic(III) and arsenic(V) are satisfactorily preserved for this time in both distilled and natural water samples at 1 and 10 µg l–1 levels at room temperature if they are stored in polyethylene or Pyrex bottles with 0.2%V/V sulphuric acid.