…low-cost water disinfecting system, which basically consists of a plastic tube and an ultraviolet light bulb, which can be run on solar power. It processes about five liters of water per minute. Ultraviolet light has been used to disinfect water for quite a while now. The inventors say the UV-Tube differs from other systems because it is inexpensive and less energy intensive. Link.
UV-Tube for Disinfecting Water