Ciliwung River is a river with a length of 199km which is located in the western region of Java, which flows through Jakarta. It is well known as the most highly polluted river in Indonesia, as shown on figure 1, due to contamination by human waste, raw sewage, industrial pollution, agricultural pollution, and household trash. When compared with other rivers in Indonesia, Ciliwung River is included as the most highly polluted river. The data is shown on figure 2. In a research conducted a few years in the past, it is proven that this river is polluted with lead (Pb) and ammonium (NH4), which was very harmful to human if consumed. The result of this research is shown in figure 3. This river has the greatest amount of lead contaminants compared to other river. The pollution of Ciliwung river can become a problem for any living organism living in the river and many people, especially for those who are living near the river. The pollution from agricultural pollution (which contains nitrates) causes abundant in number of plants, and since the plants use most of the oxygen, fishes die due to lack of oxygen. Water consumption from the river can cause people to be infected with typhoid, dysentery and cholera. People can also be infected by the Escherichia Coli bacteria which can cause diarrhea and urinary tract infection. Based on research, high number of this bacteria is found in the river. In order to obtain clean and healthy water from the river, the appropriate solution is to process the Ciliwung river in the Jakarta province into water treatment as soon as possible before the pollution gets worse. When applying this solution, the government must be involved because the Ciliwung river belongs to the government, so government approval is needed. These are the steps in water treatment, as shown in figure 4. Firstly, polluted water is collected in a large basin and the screening process takes place. When the water source is from a river, the screen serves as an important function for keeping out large natural contaminants, such as wood, fish, etc. Since the river is polluted, the screen can also be used to keep out trash. Secondly, the coagulation or flocculation process takes place. Coagulants will be added to the polluted water. There are a variety of coagulants which can be used in water treatment. Aluminium sulfate (alum) with a chemical formula Al2(SO4)3 is a chemical compound which is still extensively used in water treatment nowadays. When it is added to the water, it reacts with the water and results in positively charged ions. The positive charge ions of the chemicals will neutralize the negative charge of dirt and other particles in the water. When this takes place, the particles will bind with the chemicals and form larger particles, called floc. Thirdly, the sedimentation process takes place. During this process, floc settles to the bottom of the basin, due to its heavier weight. Then polymers will be added to the water. Polymers are used to coagulate suspended solids and produce floc. Fourthly, the filtration process takes place. After the floc settles in the bottom, the water above will pass through layers of sand, gravels, and charcoal to filter out any remaining particles. After filtration, disinfectants such as chlorine (Cl), fluoride (F-), and chloramine – monochloramine (NH2CL) (which is a compound formed through chemical reaction between chlorine (Cl) and ammonia (NH3)) will be added to the water to kill any remaining parasites, bacteria, and viruses. These disinfectants are harmful in high doses, but when they are added to water they will mix in and spread out, resulting in low levels that kill germs but are still safe to drink. The final step is the corrosion control. It is where pH is maintained by adding alkaline substances to reduce corrosion.