Levels of lead in tap water exceeding the US Environmental Protection Agency primary drinking water standard of 0.05 mg/L have been reported in several communities in Connecticut. Investigation revealed that the lead originates from leaching of soldered joints in recently constructed plumbing systems, not from source water supplies. This study examined the phenomenon quantitatively with plumbing runs fabricated from the most commonly used plumbing materials and solder formulations. Tests of two groundwater sources of different corrosivity run through soldered copper piping demonstrated levels of lead well in excess of the USEPA standard. The levels of lead declined with time and varied with the type of solder used and the corrosivity of the water. Elimination of lead in solders and education of the public are suggested as countermeasures.