What happens in this world, always happens because of some reason. Even water droplets are not an exception. As we know, water consists of H2O where two hydrogen molecules are positively charged and oxygen is negatively charged. As we know, opposite attracts each other, so water attracts more water to it and forms big droplets. In water, hydrogen bonding is much strong. These water particles along with the interface between air and water attract stronger cohesive forces. So in a water droplet, surface tension works and, as a consequence, it can change its shape as per surface level. You can witness this fact if you see water droplets on any smooth leaf like lotus leaves.
Water takes the form of a droplet not occasionally but even at the time of falling from a tap. It forms droplets and when a drop exceeds a certain standard size, it falls after detaching. On such water droplets too, surface tension works.
