Task: Question Answering
Input (English): Context: Rainwater from the roof is collected and funneled into a 25,000 gallon underground cistern . Wastewater from showers , sinks and toilets goes into underground purifying tanks and then into the cistern . The collected water then irrigates the land surrounding the house . Surrounding flowers and shrubs native to the area enable the property to blend into the surrounding rural landscape . 
Question: What might this water system be used for ?
Output (English): It may be an eco - conservation technique .