Can old plumbing be a source of lead in drinking water?

Older lead-bearing plumbing is a well-established potential source of lead in tap water, although its contribution in any particular home or apartment requires direct testing.

Clinical and environmental evidence

• Lead service lines generally contribute the greatest lead mass when present. In Flint, service-line removal was associated with an average 86% reduction in total tap-water lead mass.
• Lead–tin solder, brass faucets and fittings, galvanized plumbing, and other aging components can also release lead. Consequently, contamination may originate from the service connection, a building’s interior plumbing, or a specific fixture.
• Exposure is heterogeneous: water from different taps or apartments in the same building can differ substantially, particularly after water has remained in contact with plumbing for hours.

Corrosion mechanisms

• Corrosion releases both dissolved lead and lead-containing particles into drinking water. Release depends on water chemistry, plumbing configuration, material age, solder workmanship and exposed area, and duration of stagnation.
• Galvanic corrosion can intensify release when lead-containing materials contact copper, brass, or stainless steel: electrochemical coupling preferentially accelerates lead corrosion and can generate dissolved and particulate lead.
• Utility corrosion-control requirements reflect the importance of water corrosivity in determining lead release, but treatment does not establish that a particular residence is unaffected.

Practical implications

• A single first-draw sample cannot reliably localize the source. Testing cold water from every drinking/cooking fixture through an EPA- or state-certified laboratory is needed to establish whether water contains lead.
• Sequential sampling after at least 6 hours of stagnation can help distinguish fixture or premise-plumbing contributions from potential service-line contamination. Flushing may reduce exposure after stagnation, but the necessary duration is site-specific and does not remove the underlying source.
• If personal exposure is a concern, venous whole-blood lead is the preferred clinical measure; urinary lead does not reliably identify water or plumbing as the source.

Bottom line

• Old plumbing is a scientifically credible but unconfirmed source until fixture-level water testing demonstrates lead.