Rainwater harvesting systems are a great idea, and relatively simple to set up. But debris and contamination can be a problem. In this article, we discuss why it is important to keep leaves and bugs out of your tank. When leaves collect in your water after falling off the tree, they will decompose and therefore pose as a threat to the quality of your water (not to mention fueling algae growth). Bugs like mosquitoes carry diseases and they also breed in stagnant water.