Illustrative (not real) image of the system.
More than 2.1 billion people still lack safely managed drinking water. For them, and for many others living through disasters or infrastructure failures, making water safer often means choosing between imperfect options.
Boiling water takes fuel, which costs money. Chlorine tablets can leave an unpleasant taste and do not remove many chemical contaminants. Filters can clog, break, or become too expensive to replace. Modern devices exist, but most depend on consumables, batteries, and maintenance.
Now, a team of researchers has built a small floating capsule that combines several steps into one and doesn’t need external power. Described in Nature Water, the device works when you shake it by hand. This powers a sensor to estimate chemical risk by measuring total dissolved solids, sends the result by Bluetooth, and disinfects water as it bobs on the surface.
It doesn’t use a battery, a solar panel, or chemical additives. It’s powered by a magnet that moves through a copper coil when the user shakes it, generating enough current to run a tiny sensor and Bluetooth chip. It needs just three seconds of shaking to start working.
A New Way to Sterilize Water
The capsule begins with a quick safety check. A user shakes it by hand for about three seconds. Inside, a small magnet moves through a copper coil, generating enough current to power a tiny sensor and Bluetooth chip.
That sensor measures total dissolved solids, or TDS. In simple terms, TDS is the amount of dissolved material in the water, mostly ions such as salts and minerals. The researchers use it as a rough warning signal for possible chemical contamination.
If the water measures below 250 milligrams per liter, the device treats it as low-risk for dissolved contamination and proceeds to doing microbial disinfection. If the reading is higher, it flags the water as unsuitable, because killing microbes wouldn’t necessarily remove chemical hazards.
Once it is floating, the capsule uses a second kind of electricity.
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As the device moves up and down, water repeatedly touches and pulls away from its plastic shell. This creates a small electrostatic charge, similar to the static that builds up when you rub a balloon against hair. The water surface becomes positively charged, while the capsule’s plastic surface becomes negatively charged.
On the outside of the capsule are electrodes coated with tiny conductive polymer nanorods. These rods are only about 40 nanometers wide, and their sharp tips concentrate the charge into very strong local electric fields.
Those fields are strong enough to damage microbes nearby. They open tiny pores in bacterial membranes and viral shells, a process called electroporation. In the study, this killed bacteria and eliminated virus-like particles without adding chlorine or any other chemicals.
Microscopic images of microorganisms before and after sterilization using the capsule developed by the research team. Provided by Yonsei University.
It Works, Within Limits
The researchers tested the capsule against common lab organisms, including Escherichia coli, Bacillus subtilis, and MS2 bacteriophage, a virus surrogate often used in water studies.
In one-liter samples, the capsule removed E. coli and MS2 within 20 minutes. B. subtilis took about 25 minutes. In tap water, river water, and lake water, complete disinfection was achieved within 30 minutes for one-liter samples. Four liters of river water took 52 minutes.
The team also tested durability. The capsule maintained its performance through 120 repeated disinfection cycles in four liters of river water, and the researchers reported almost no harmful byproducts. The estimated manufacturing cost is under $25, and that could fall if production scales up.
That makes the device especially interesting for disaster response, remote communities, and places where batteries, electricity, or chemical disinfectants are hard to obtain.
Still, an important limitation remains: this device kills microbes, but it doesn’t remove every dangerous contaminant. It cannot replace proper water testing in areas affected by industrial pollution, mining runoff, arsenic, pesticides, or chemical spills.
Professor Sang-Woo Kim of Yonsei University, who led the work, framed the device as a self-powered water safety platform.
“We have developed a new concept of a self-powered water safety platform that can verify potential contamination right before drinking and remove pathogenic microorganisms without external power or chemicals,” adding, “This technology can help improve access to safe drinking water in areas with limited power infrastructure and in disaster situations.”
The research results were published on the 8th in the international journal Nature Water.