About 50 mL of the tap water was placed into a polypropylene flask and delivered to the laboratory on the same day. For iodine analysis, the samples were stored "as is" at 4 ºC for less than 2 weeks (the stability of iodine under these conditions was previously investigated by ). For macro-element analysis, sample aliquots were acidified with 65% HNO3 (to 1% HNO3 in each sample) and then stored at room temperature.