Lead usually comes from the pipe, not from the water source.
What it is
Lead is rarely in groundwater or in the water leaving a treatment plant. It gets into drinking water from lead service lines, from lead solder used in copper joints before 1986, and from brass fittings and older fixtures. Michigan's Lead and Copper Rule sets an action level of 12 parts per billion, which is tighter than the federal 15.
What it usually does
Nothing detectable at the tap. There is no taste, smell, or color. How much comes off the pipe usually depends on how long the water has been standing in it, how warm it is, and the pH and mineral content of the water, which is why the same tap can give very different results at different times of day.
What it does not prove
A single number from a random pour usually settles very little, because the result depends heavily on how the sample was drawn. A first-draw sample after six hours of standing and a sample taken after running the tap for two minutes are measuring different things, and both are legitimate for different questions. A low result on a flushed sample does not establish what the first glass of the morning contains.
When to test
Usually worth testing in any house built before 1986, in any house with a lead service line, and whenever a young child or a pregnant person lives there. Follow the lab's sampling instructions exactly, since the drawing procedure is part of the test. Your utility can usually tell you the service line material on record.
See what this usually means for your water.
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