Most people know that lead is toxic, and so many people are baffled as to how it gets into the water supply. Yet the reality is that lead has been used in plumbing since the days of Ancient Rome; “in fact, the word derives from the Latin word for lead, plumbum,” notes Ben Paynter (2016, p. 93). It was widely used in the water infrastructure that built the U.S., because as Paynter states, “lead pipes solved a lot more problems than they caused.” Unfortunately, this has left us with a lead legacy in our water systems.

How much lead is allowed in water?

Current standards require utilities to take steps to address the problem if lead levels exceed 15 ppb in 10% or more of residential taps tested. However, most safety experts consider anything above 5 ppb to be toxic, and since no amount of lead is known to be safe, even a few parts per billion of lead is a few parts too many.

How does lead get into the water supply?

There are two possible ways. One is if the water was already contaminated with lead to begin with, and the system fails to adequately filter it. This can happen if it were drawn from a polluted source such as a dirty river or a well near a fracking site that allowed heavy metals to leach into the groundwater.

More commonly, however, lead contamination occurs on the latter end of the system, as water flows through lead service pipes or fixtures in the home. If the pipes are degrading (which happens naturally over time and is worsened by corrosive water), lead can heavily contaminate the water coming from the tap.

This is also why lead levels can vary so greatly even from one home to the next in the same neighborhood: It all depends on the condition of the pipes leading from your home to the water main. The 75 million homes built before 1980 (more than half of the nation’s housing units) are most likely to contain some lead plumbing. And around 7.3 million homes built before 1986 are connected to water mains through lead service lines, which engineering professor Marc Edwards says is like passing water through “a pure lead straw.” Lead service lines were typically laid down before the 1930s, so they are more common in major cities. But some communities continued to install such pipes for decades after that. Replacing these service lines can cost thousands of dollars, and typically must be paid by the homeowner. In March 2016, the National Drinking Water Advisory Council recommended that all U.S. cities replace their lead service lines – a feat that would cost upwards of $50 billion dollars.

The scope of the lead water problem in the U.S.

One examination by USA Today found nearly 2,000 water systems across all 50 states had lead levels exceeding the EPA’s threshold of 15 ppb. Six hundred of these had tests exceeding 40 ppb. This included some major water systems, such as the Passaic Valley Water Commission, with about 315,000 customers in northern New Jersey, and New Bedford, Massachusetts, serving about 95,000. (Young & Nichols, 2016)

Overall, around 20% of the water systems nationwide test above the 15 ppb levels considered safe for lead. (Ungar, 3-21-2016)