Water that returns to streams and rivers after it has been put to use is called a return flow. In most cases when water is used, not all of it is consumed and the remainder is returned to lakes, rivers or streams. When irrigating fields, for example, some water will typically flow off the land, referred to as tail water, and return to a waterway. Another portion will return after seeping into the ground, slowly percolating back to streams as groundwater. In municipalities, most of the water used in homes flows to wastewater treatment plants, where it will be treated and returned to a water source.