Originally Posted by rowan

You still have the "pay for x% sewage discharge when it's actually evaporated into the atmosphere" issue with swamp coolers. I'd say the water usage with the roof spray system would be similar or less than a swamp cooler. The controller has various sensors to figure out the right amount to spray: just enough so that there's ALMOST beading and a dribble of water running down the tiles. If it's working properly then no misted water ever ends up going down your drainpipe. OTOH, a swamp cooler needs to flush or bleed its sump regularly to prevent buildup of mineral deposits.