Rainwater Harvesting You can calculate how much Rainwater usually get wasted. How much Rainwater you can collect from Individual Rooftop? Say for example: If Rooftop Area = 1200 sq ft (111 Sq mtr) Annual Avg. Rainfall = 800 mm Runoff coefficient = 0.90 Total Rainwater collect = 79920 liters annually.( Means in 3 months) mostly Rainy seasons. Harvest Rainwater with Rainy Rooftop Rainwater Harvesting Filters. We have four different Models FL - 100 ( Roof Area Upto 1200 Sq ft) FL - 200 ( Roof Area Upto 2400 Sq ft) FL - 300. ( Roof Area Upto 3600 Sq ft) FL - 500 ( Roof Area Upto 5000 Sq ft) We are providing total Rainwater Harvesting solution In Surat, Vadodara, Ahmedabad, Anand, Bharuch, sanand, kadi.