Access to safe drinking water is a human right, but in many parts of the world that’s more wishful thinking than a reality. Researchers now might have developed a new tool that could help remove dangerous bacteria from drinking water.

The method, published in ACS Applied Materials & Interfaces, employs a newly developed microbot that can move and kill off pathogenic bacteria like E. coli. The microbots are spherical with one half covered in magnesium and the other in gold and iron with nanoparticles of silver attached.

The microbots are called Janus, after the two-faced Roman god, and their two-facedness is actually really important.

When the microrobots are dropped in water, the magnesium reacts with the liquid, creating bubbles of hydrogen gas and propelling the Janus forward. As they move through the water, bacteria stick to the gold and are quickly absorbed by the silver nanoparticles. Bacteria, just like fantastical monsters, are killed by silver. By moving around the water sample, the robots maximize their chance of coming in contact with as many bacteria as possible.

The team tested the microbots in the lab and found that the magnesium was enough to have the Janus move around a sample of water for 15 to 20 minutes. After that, the magnesium is spent and the Janus bots are removed from the water with a simple magnet, hence the inclusion of iron in the robot.

The test showed that in water spiked with a large number of E. coli, the microbots were able to kill off more than 80 percent of the bacteria. This is more effective than other silver nanoparticle approaches (which are less than 35 percent effective), and thanks to the magnetic properties of the Janus bots, they are easier to remove from water than common disinfectants.

The issue with disinfectant is not just removing it from the water, but that bacteria can develop a resistance to those products, so they need to be used in combination with other disinfectants or in higher doses, which might generate harmful byproducts.

These bots could be ideal in places where water is scarce, as well as in places where other sterilizing methods mean losing precious water.