In 1986 the EPA/DPH instituted a 0% lead standard for solder used to adhere copper piping in plumbing structures. Generally, lead based solder is the most common source of lead in water supplies well or municipal. When water is idle between usages, lead being a very soluble metal gets absorbed into the water at elevated levels. So in houses built before 1986, the longer the period between usages of a faucet, the greater potential that the first 0.5 gallons of water from the particular fixture has an elevated lead level. Due to this fact, it is highly recommended to run the water for a couple of minutes before usages in houses with aged plumbing. Since lead is rarely a source issue, by running the water for a few minutes the water is passing through the plumbing so fast lead cannot be absorbed.
This being said, to ensure the homeowner is aware of their potential exposure to lead, proper sampling should be performed by a licensed professional. There are two types of sample collection procedures; a first-draw sample and a flushed sample. The first draw sample should be collected from a usable faucet that hasn’t been used for the prior six hours but no longer than twelve hours. The first few cups that come out of the faucet are collected. The purpose of this collection is designed to replicate the longest time a fixture would be idle in a lived in house. This sample will yield a result of maximum exposure to lead. The flushed sample is then collected after the water has been running for a few minutes (typically till it runs cold). This will yield a result of your true exposure to lead. In addition, low pH value waters can cause lead to leach into the water at higher rates than normal.
It is common to have high levels in a first draw sample and negligible levels in a flushed sample in houses built before 1986. If there are lead levels present in a sample collected from a house built post-1986, then the only other potential source would be the particular fixture the sample was collected from. Some higher end and foreign made fixtures can have a lead base to the plating or brass fittings used to install them. Further sampling can be performed to confirm if this is the case. Otherwise, the fixture should be replaced or a filter for lead should be installed at the area in question.
To learn more about treatment options for lead in water, please refer to: