According to the World Health Organization, there are at least 1.7 billion people in the world today who drink water contaminated with faeces, putting them at risk of diseases including diarrhoea, cholera, dysentery, typhoid, and polio, with diarrhoea alone causing around a million deaths per year. If you live in a country where this isn’t a problem, it means that the generations before you invested massive amounts of time and money into building sewers, wells, water treatment plants, reservoirs, and all the rest of the infrastructure that we should be grateful for every time we turn on the tap.

Where this infrastructure doesn’t exist, there are other solutions. One of these is to treat water using UV light to kill harmful bacteria. This solar water bottle by Aarav Garg and Riddhi Gupta comprises a 3D-printed body with a circular 6 V 80 mA solar panel and two UV LEDs housed in the screw-on cap. We’re fascinated by the simplicity of this project. We know that it’s not massively scalable, but this is a fascinating approach to an eternal problem.