Conventional Rainwater Systems gather run-off rainwater for ecological running, domestic, and agricultural use. Rainwater systems can be drawn back to ancient civilizations who would collect water falling on their roofs in a process called rainwater harvesting. Of late, rainwater harvesting has improved in popularity as people begin searching for more workable buildings. However, a bulk of water systems today are still not worried about harvesting rainwater; instead, most water systems transport the rainwater to bodies of water through gutters, inlets, and storm sewers. Conventional rainwater systems divert rainwater into bodies of water in order to prevent flooding. Gutters, ditches, and other small scale water relocation devices are often called minor rainwater systems. The main resolution of these minor systems is to collect rainwater from the roofs of buildings and transport it to larger systems that can handle larger volumes of water. Gutters and downspouts are one example of minor rainwater systems larger rainwater systems are typically called major rainwater systems. Rainwater systems typically are used to both transport and filter large amounts of rainwater. Examples of major rainwater systems include storm sewers, water retention ponds, and water treatment plants. Occasionally, rainwater is treated before it is discharged. One of the simplest ways to treat rainwater is by using a water retention pond. The primary objective of a water retention pond is to reduce the peak rate of surface runoff like a water detention pond. The second aim of a water retention pond is to remove some of the pollution in the water. In addition to using retention ponds, rainwater could also be treated by diverting the water to a wastewater treatment plant where the rainwater would be combined with sanitary waste. Treating rainwater is a good way to promote sustainability because untreated water can contain hazardous chemicals like motor oil and pesticides that may harm the environment. Ancient civilizations have been using rainwater harvesting systems for thousands of years.