Homeowners whose local governments have replaced lead water pipes may be alarmed by new research that has found pipes that contain sections of both lead and copper could actually be more detrimental to the public health.

Before lead was identified as a dangerous contaminant that can cause stomach pains and long-term brain damage if ingested, many municipal water systems used lead water pipes. Communities across the country began replacing them in the 1970s, so homes built after that are unlikely to have lead pipes – though a home inspection conducted by a company with knowledge of plumbing may be able to reveal the presence of lead pipes for homeowners who are unsure.

However, local governments have no authority to mandate that homeowners replace lead supply pipes located on their property. Since few American homeowners – 10 percent – consent to this change, pipes leading to some older homes are comprised half each of lead and copper.

"Since you started with a whole lead pipe and you now have half a lead pipe, you might think your problem would be half of what it was or – maybe – completely unchanged," Washington University in St. Louis professor Dan Giammar said in a press release.

Research led by Giammar has found that when lead and copper pipes are conjoined using brass connectors, the amount of lead in drinking water can increase by about five times what it was when pipes were only lead. This occurs because of galvanic corrosion, which results when two dissimilar metals are exposed to liquid.

This research could undermine years of Environmental Protection Agency (EPA) regulations aimed at controlling lead and copper contamination in tap water. The EPA passed its Lead and Copper Rule in 1991 to compel more monitoring of lead and copper levels in water. If counts of either of these metals exceed certain limits, pipes must be replaced.