In the future, contaminated water may be made drinkable not through the addition of harsh chemicals, but by pouring in a bucket of swimming robots instead. European researchers have developed spherical microbots that could do just that, swimming around under their own power to catch and kill deadly bacteria before being easily removed from the water.

Normally, water is cleaned with a generous dose of chlorine or other strong chemicals. The problem is they can have ill effects on people, and don't always kill some of the toughest bugs anyway. Adapting previous work with self-propelled swimming microbots, Spanish scientists has now pitted them against bacteria to test their merits as a chemical-free purification system.

The team's microbots are quite cleverly designed, taking clear cues from the Janus particles developed last year by a Max Planck team. But where those two-faced microbots would automatically steer themselves towards light sources, the new ones are powered by chemical reactions and have been given antibacterial weapons.

The particles are similarly two-faced, with one half made of magnesium and the other a mix of iron, gold and silver. The magnesium side provides propulsion, since it reacts with the water and creates hydrogen bubbles. The other side, now the front of the moving particle, is designed to scoop up and kill microorganisms, which stick to the gold layers and are destroyed by the silver nanoparticles.

To test the microbots, the researchers added them to water that had been spiked with high levels of E. coli. The magnesium fuel lasts about 15 to 20 minutes, and during that time the particles were able to kill over 80 percent of the bacteria. Since it's probably not healthy to be drinking water full of tiny robots, they can then be easily removed with magnets, thanks to their iron layers. The researchers also say the microbots don't leave any other harmful waste in the water.

The study was published in the journal ACS Applied Materials & Interfaces. The microbots can be seen in action in the video below.