Half of the natural disasters are due to floods of all kinds, leaving thousands dead and injured, as well as costly material damages. An early warning system (EWS) is a vital tool to reduce disaster risk but requires components that allow rapid communication and effective response of people at risk. Contribution of advanced technology has been fundamental in the prevention of catastrophes, but unfortunately, its high cost, among other factors, does not allow its coverage to reach developing countries or to communities in areas of higher vulnerability. This was evident in Colombia, where EWS exists for large-scale phenomena, but where river floods in poor municipalities meant the country's greatest tragedies in recent years. Hence the importance of designing the self-sustaining early warning system in river currents, since it combines state-of-the-art but low-cost technological elements, allowing it to operate autonomously from alternative energy sources, continuously and accurately measure the current fluvial level, and send real-time alert signals via high-speed and efficient wireless communication protocols. Construction of a prototype of the system made it possible to test and verify the functionality and efficiency of the monitoring stations, both in accuracy and speed in measures of increasing water levels, as well as in the rapid communication of alerts to an end-user, through cell phone text messaging.