Contaminants

Lead in drinking water: why the pipe matters more than the plant

Every other contaminant on this site is a question about your water system. Lead is a question about your house.

Where it actually comes from

Lead pipe was standard plumbing material for most of American urban history. It is soft, easy to bend, resists pinhole corrosion and lasts a century. Cities installed it by the millions of feet, and the Safe Drinking Water Act amendments did not ban it in new plumbing until 1986.

The pipe that matters most is the service line: the short run connecting the water main in the street to the building. It is often partly the utility's property and partly the owner's, which is one reason replacement has been slow. Lead also appears in solder joining copper pipe, in brass fixtures, and in older faucets.

None of this is upstream of the treatment plant. It is all downstream of it, which is why lead is regulated at the tap rather than at the point where treated water enters the system.

Why it dissolves at all

Lead pipe does not release lead continuously. Under stable conditions a mineral scale forms on the inside of the pipe and acts as a barrier between the metal and the water. Utilities maintain that barrier deliberately, usually by adjusting pH and adding orthophosphate, in a practice called corrosion control.

When corrosion control lapses or the water chemistry changes, the scale destabilizes and lead enters the water. This is what happened in Flint, Michigan in 2014: the city switched source water without applying corrosion control to the new supply, the protective scale broke down, and lead levels rose sharply. The pipes had been there all along. What changed was the chemistry running through them.

What the numbers mean

Lead is regulated differently from most contaminants. Instead of a Maximum Contaminant Level it has an action level, which is not a health threshold but a trigger: when more than 10% of sampled homes exceed it, the system must take specified steps.

The health goal is zero. The action level is a feasibility judgment about what systems can be required to achieve, and the gap between the two is the point: being below 15 ppb is not the same as being safe.

The rule that changes things

The EPA finalized the Lead and Copper Rule Improvements on 8 October 2024. It requires water systems to inventory their service lines and replace lead ones, with most systems working to a ten-year replacement schedule beginning in October 2027. Systems with an unusually high proportion of lead lines may receive extensions.

The practical consequence for a homeowner is that your utility is now obliged to know whether the line to your building is lead, and to tell you. Many have published searchable inventories. That is the first place to look, and it costs nothing.

Who is most at risk

Lead affects the developing nervous system, and the exposures of greatest concern are in pregnancy and early childhood. There is no identified safe level of lead in children's blood.

The risk factors that matter are structural rather than geographic: housing built before 1986, and especially before the 1950s; a known or unknown service line material; and long periods of standing water, since lead accumulates in water that sits in the pipe overnight.

What to do

1. Find out what your service line is made of. Check your utility's published inventory first. If it is unlisted, the utility is required to be working on it.
2. Test at your own tap. A certified laboratory testing a first-draw sample is the only way to know your number. System-level data cannot answer this.
3. Flush before drinking if water has been standing for hours. Run the cold tap until it turns noticeably colder.
4. Use cold water for drinking and cooking. Hot water dissolves lead more readily and has been sitting in a heater.
5. If you filter, filter for lead specifically. A filter certified to NSF/ANSI 53 for lead reduction works. One certified only for taste does not. The same distinction applies to filters marketed for PFAS.