"Back watered" refers to the action of water backing up, stagnating and forming a still pool. Antonyms for back watered would be words that describe the opposite action, such as "flowing", "running", "streaming", "surging", or "gushing". These words indicate a rapid movement of water, rather than a sluggish one. A flowing stream or a surging river implies a continuous and dynamic movement of water. These antonyms help to paint the picture of a lively and energetic body of water, rather than a stagnant, back watered pool.