Table of ContentsIssues and Factors Affecting Rainwater Harvesting of Commercial BuildingsRoofing MaterialLand Use PatternIntensity and Duration of PrecipitationWeather ConditionsIneffective Use of Prime Systems flushingIn the field of civil engineering we have to consider not only structural elements, bridges, highways, railways etc. but also in the field of water and the environment. When we think about water resources. It is especially a very essential resource in everyday life and also in the future due to its demand for sustainability. And also, when we think about ethics, we must also pay attention to not only the use but also the protection of this resource and its maximum use. There are certain methods to protect water resources and reuse this resource. Rainwater harvesting is one of the best methods to protect this water resource. In reality, there are mainly two methods for harvesting rainwater. Harvesting by runoff and harvesting on roofs. Precipitation intensity is the amount of water that falls in a given period. When we talk about this situation in Sri Lanka. According to the data released by the irrigation department in 2017, the data is as follows: “Say no to plagiarism. Get a tailor-made essay on “Why Violent Video Games Should Not Be Banned”? Get the Original Essay 103 River Basins Major River Basins Mahaweli-1027 km2 Walawe -2442 km2Kalu -2772 km2Average Annual Rainfall -1861 mmAnnual Rainfall Volume -12x1010 m3 (DATA FROM IRRIGATION DEPARTMENT IN 2017) Sri Lanka, as tropical country, mainly receives rain in three main ways. Monsoons North East Monsoon South West Monsoon Convective Cyclonic So rainwater harvesting is a very important criterion because according to the annual rainfall of 12x1010 m3 we use very less quantity of water. Over the past period, Sri Lanka has paid attention to this matter. Once upon a time, King Prakkramabahu said: "Do not drop a very small quantity of water from the sky without using it directly towards the sea. When considering the method of harvesting, it is defined as storage in such a way that it can be used in the future. For the harvesting method, we must have a suitable catchment. The best method is to take the crop from the roofs and use it for domestic and agricultural work. In Sri Lanka, as in the world, we are currently experiencing a water shortage. Precipitation patterns have been confused. People in rural areas do not have running water. Natural water resources are not qualitatively and quantitatively capable of meeting water demand. The problem of drinking water is all the more critical as hundreds of people have died due to the CKDu problem in the North Central province, consuming poor quality water. Rainwater harvesting is therefore a better solution to overcome these problems. Due to the increase in human population, their basic needs have also become important. Therefore, the demand for drinking water is increasing day by day. However, nature has been able to provide humanity with a quantity of pure and natural water. But after the industrial revolution and thanks to the development of new technologies, humanity became very concerned about the environment. Water was avidly used by some countries for industrial purposes, while others suffered from water scarcity. Many natural disastersare produced around the world. Climate models have changed. Environmental problems such as global warming have emerged. Natural water resources were polluted as industrial wastes were dumped into surface waters without any treatment. Their water quality declined rapidly. Therefore, the amount of natural water resources was not sufficient to meet every human's demand for drinking water equally and efficiently. Although there are many water resources on this earth, only a significant percentage is drinkable. This drop of water has also been polluted by man. A water shortage was created on this planet not because of any living being but because of humanity. According to the United Nations Department of Economic and Social Affairs, approximately 700 million people in 43 countries today suffer from water scarcity. By 2025, 1.8 billion people will live in countries or regions facing absolute water scarcity, and two-thirds of the world's population could live under conditions of water stress. Some people have to walk hundreds of kilometers to find even a small amount of water to drink. People tend to drink polluted water to meet their drinking water needs with the water they have. It is not suitable for drinking consumption. But they have to find water any way they can to quench their thirst. Due to the consumption of this polluted water, they suffered from many water-borne and water-related diseases. Thousands of children and adults have died from drinking polluted water without treatment. It was found that the problem of CKDu is also caused by the consumption of polluted water contaminated with heavy metals. People then tend to find solutions to this water shortage and save humanity from this burning problem. A rainwater harvesting method can be obtained. It is defined as being stored in such a way that it can be reused later. For harvesting method, we should have proper catchment, mainly two methods for runoff harvesting and roof top harvesting. Rooftop harvesting is a good method not only for households but also for agriculture. Certain factors must be taken into account when collecting rainwater on roofs. When considering the situation of Sri Lanka, in June 2005, the Government of Sri Lanka adopted the “National Rainwater Harvesting Policy and Strategies” with the aim of encouraging communities to control water near its source by collecting rainwater. Accordingly, the intended objectives were increased water security, minimizing the use of treated water for secondary purposes, reducing flooding, improving soil conservation and water recharge. underground, provision of water for domestic use with adequate treatment, agricultural benefits and reduction of energy consumption. In addition to this policy, a regulation was published in the Official Gazette on 17 April 2009, which makes rainwater harvesting compulsory in certain categories of new buildings in areas under the jurisdiction of municipalities and urban councils. As a result, rainwater harvesting systems have been installed in several places in Sri Lanka. and they came from different types of rainwater harvesting tank materials. And also, they would either be above ground or underground or alternately. Even though it is widely used in the dry zone, there are some problems in rainwater harvesting systems in Sri Lanka. The quality of stored rainwater is.