Water is one of the most sustainable resources in the world, offering an abundance of hydro energy. Getting a large amount of electricity through conventional water energy harvesting is expensive, with complex mechanisms and bulky installation systems. In the case of the small amount of energy for some portable electronic devices and sensor systems, water droplet harvesting as a sustainable energy resource has become a forward‐looking step to meet the future demand for green energy. The ultimate demand for green energy in the future requires all the possible sustainable energy sources surrounding human society. The emerging potential of water droplet‐driven energy‐harvesting nanogenerators can meet a significant portion of the green energy demand. In this review, the recent developments in droplets‐driven nanogenerators for effective energy scavenging is summarized. It also includes an extensive discussion about the device structures from the material selection and output performance aspects. This review also gives a brief discussion on the applications of droplet‐based nanogenerators and outlines the future possibilities via the current improvement in designs and fabrication strategies that have been introduced by the field.

information and communication, [11] environmental monitoring, [12,13] security system, [14] and more are going through a revolutionary change.One of the significant drawbacks of a typical sensor is the external power supply, and sometimes it reduces the portability option of the sensing devices. Therefore, self-energy sources are the primary requirement for sensing technology to make it more portable and usable from anywhere or any place. Currently, replaceable batteries are standard for supplying energy in devices and sensors. However, the characteristics of batteries limit the flexibility and portability of sensing devices. Meanwhile, the limited lifetime of batteries is responsible for environmental pollution, which does not conform to the principle of sustainable development. As a result, colossal research going through the last decade to develop energy sources that harvest available ambient energy sources present in nature, [1] such as mechanical energy, chemical energy, thermal energy, and more to convert them into electrical energy, drive devices, and make it self-powered. However, much technological development has already been achieved to successfully harvest this abundant energy source from nature to drive the self-powered sensor system and devices.Triboelectric nanogenerator (TENG), based on contact electrification and electrostatic induction, is a powerful technology to convert mechanical energy to electrical energy. It can directly transform mechanical energy into electrical energy, efficiently operating the various self-powered sensors. Therefore, TENG technology has already provided effective power solutions for motion, tactile, and pressure sensors for diverse application sectors, such as biomedical and healthcare, robotics, human-machine interfaces, smart city and home, and cybersecurity applications.Piezoelectric nanogenerator (PENG) is another significant energy harvesting technology that transforms low ambient mechanical energy into electrical energy. Piezoelectricity is generated during the deformation of piezoelectric materials. Typically, when mechanical force is applied in non-centrosymmetric crystalline materials, it alters the distance between positive and negative charges and creates electric dipole moments or charges. So, it is suitable and adequate to harvest piezoelectric energy using mechanical force, which can easily power the sensors and devices for real-world applications like healthcare monitoring, robotics, intelligent traffic sensor, and artificial intelligence application.Thermoelectric nanogenerators (ThNGs) utilize the ambient and low-quality waste heat from the environment and convert it With the rapid technological development, self-powered sensor systems that are capable of operating without an external power supply are becoming more and more crucial in the field of sensing and detection. One of the major drawbacks of a typical sensor is the necessity of an external power supply or batteries, which makes sensor systems more complex and less handy for mobile devices. In t...