Bacteria can thrive in p-traps, those “U bends” below sink drains that collect everything from errant earrings to lost toothpaste tube caps. That’s a big problem, especially in hospitals where sinks have been linked to a slew of bacterial outbreaks. To determine exactly how the pathogens spread, scientists built a row of five sinks in a setup similar to that in many hospitals, with all of them draining into the same pipe. After sterilizing all the sink components and separating the countertops with Plexiglas shields, the scientists seeded p-traps with harmless, fluorescent bacteria to see where the microbes traveled. With the daily addition of a nutrient broth to mimic liquids commonly poured into hospital sinks—like extra intravenous fluid and leftover beverages—the bacteria flourished, shimmying up the pipe at a rate of about 2.5 centimeters per day to contaminate sink drain covers. There, faucet water splattered the bacteria around the sink bowl and countertop, the team reported last week in Applied and Environmental Microbiology. Moreover, with only one sink’s p-trap contaminated, running water alone—with no nutrients—was enough for the bacteria to infiltrate three other sinks through the common drainpipe in just 1 week. The researchers’ next move: tracing how bacteria make the leap from sinks to patients.