Raindrop makes in still water are circles why do they make circles?

Waves transfer energy outward equally. Since there is no barrier to the water, when a raindrop hits the water that energy of the raindrop falling has to go somewhere, the energy is transferred from the raindrop to the water and goes outward from the epicenter (where the raindrop fell). The waves (circles) will continue to travel an equal distance unless there is an outside force such as wind, another object, ect. to stop the wave