Comparing the total iodine concentration in tap water samples with Lake Kinneret water, we may conclude that groups C and D probably contain a higher percentage of water from this source than from others (Table ). The hardness of C group waters is much higher than that of Lake Kinneret water, which suggests the use of local well water. Our data presented in Table are in agreement with the values published by Dreizin et al. ( ) which approximately estimated the hardness of natural waters in Israel as 250-350 mg L - 1 (our range is 190 -632 mg L -1 ), and Lake Kinneret water (the main source of NWC) as 200-245 mg L -1 (our result is 245 mg L -1 ).