How Major Cities Keep Their Water Clean

An unsafe water

An unsafe water supply can cause severe illness and even death. John Snow, who discovered that the bacterium that causes cholera was spreading through the water pumps in London, noticed this link in the mid-nineteenth century.

How Major Cities Keep Their Water Clean

How Major Cities Keep Their Water Clean

It must be treated to kill bacteria, viruses and protozoan parasites in order for it to be safe for humans to drink.


Water sources used and treated for human consumption include storage reservoirs (dams) and rivers. The city of Dublin for instance is a major city which has a population of over 1 million people and it collects over 540 million liters a day from rivers. It is treated at 4 water plants in four main stages – coagulation, sedimentation, filtration and chlorination.

As water is taken in from the river, debris is captured on fine mesh screens. It is then treated with alum which attaches to smaller debris that has managed to pass through the screens.  This then falls to the bottom of the tank creating a layer of sediment. The clear water is then poured through several sand and gravel filters. These filters help to remove any more particles that are still present. After this filtration stage comes to an end it is then subjected to a chlorination process. In other words, chlorine is added to ensure that any microorganisms are killed off so that what you get through the tap is clean, drinkable and uncontaminated.

US Cities

These same four steps of water treatment are used in the United States. What is important to realize is that the exact methods will vary slightly among different cities depending on the source. Groundwater is generally easier and quicker to treat than surface water. Water in rivers and dams will of course have large amounts of sediment present. In some parts of the world, such as the United States, fluoride is also added to the drinking water though the extent of fluoridation varies widely from place to place. Apparently, this addition has actually helped to reduce the number of people with have tooth decay, and so is considered a major benefit to overall health. Tap water in New York City is very clean but some people live in old buildings with lead pipes which means that it can leach into the supply. Lead poisoning is potentially deadly so be careful if you live in areas where pipes are in poor condition. Much of the water in New York comes from the watershed in the Catskill Mountains, and even though it is very clean in comparison to other regions, it is, however, still chlorinated to ensure that it is not contaminated with dangerous microorganisms.

Many major cities are generally able to keep their drinking water clean using this four-stage process during which sediment is removed, is filtered several times and when chlorine is added. Any breakdown in the cleaning process could pose a health risk to people which is why we should take water sanitization so seriously.