PVC Unit flow wood India tiles roofs strain people floods bamboo system reliance Benefits monsoons plastics building downpipes challenges dependency components Empowerment maintenance temperatures roof gutters metal sheets storage tank summer months climate change Sustainability water shortages galvanized iron watering gardens various purposes southwest monsoon water availability total precipitation Environmental Impact limited time duration suitable roof surface simple infrastructure Allegiance Enterprise traditional water sources Allegiance Water Management potable household activities Rooftop Rainwater Harvesting existing water infrastructure erratic precipitation patterns Rain Water Harvesting Solutions