In the mid-1970s, NASA partnered with a company known as Umpqua Research to figure out a water purification system for the Space Shuttle. The result was the MCV, or Microbial Check Valve—a system that dispensed iodine to kill off water-borne bacteria.
Since then, NASA has iterated on the technology, most recently creating the Regenerative Environmental Control Life Support System.
The size of two refrigerators, the system can support up to six people aboard the International Space Station with chemical adsorption, ion exchange, and ultra-filtration. While designed for space, the system is also perfect for developing regions where water may be heavily contaminated, or (on a smaller scale) for use in your home.
Image source: Spinoff Magazine, 1995