More than 70% of Earth is covered with water. Yet, 96% of the water resources are located in oceans and seas with a high salt content. As a result of global warming, more and more people lack access to clean drinking water, especially in regions where they are least able to act against this threat. We develop an approach to enable people in affected regions to self-supply with water at low cost. We use thermally switchable hydrogels that swell in water at a low temperature and retain salt, while they de-swell at a higher temperature and release water. With that, the temperature difference between day and night can serve to drive the process; naturally and free of charge, for people and for a human right: access to water.