A grass and soil filter was tested in Tucson to clean up urban runoff. The filter was made of grass and soil, and it helped reduce pollutants like chemicals, bacteria, and sediment in the water. The filter worked by letting the runoff flow over it, and the water quality improved as it passed through. The researchers found that the filter was effective in cleaning up the water, especially when the grass grew more and the soil settled. This study shows that using grass and soil filters can help manage water quality in urban areas.