This article is considered accurate for the current version of the game.
There are three types of pollution in Cities: Skylines; ground, water, and sound pollution. Ground and water pollution share one info view, while sound pollution has a separate info view
Ground pollution is caused mainly by industry, while the farming and forestry industry specializations don't cause ground pollution at all. Some of the Farm Area and Forestry Area buildings from the Industries DLC do create some pollution. It is also caused by other polluting buildings, such as fossil-fuel power stations and incinerators. Pollution will affect the ground immediately underneath the polluting buildings, as well a small surrounding area. Even if the source of the pollution is removed, it will take some time for the ground to return to an unpolluted state. If non-polluting buildings have uncollected garbage for a long time, they will also pollute the ground.
Ground pollution can be observed as discoloured ground, as well as in the pollution info view. Residential zones should not overlap with polluted areas as Cims who live on polluted ground will get sick. Water towers should definitely be kept away from such areas, otherwise the pollution will contaminate the water supply and cause a city-wide health crisis.
- Main article: Water and sewage
Virtually all buildings produce sewage. Assuming you have have a decent water grid, this sewage causes no issues for any given building, and it instead is transported through the same pipes through which water is brought into the city. Having pipes containing both clean and contaminated water has no negative effect. The pipes should lead to an outflow where the polluted sewage is drained into a body of water. Water drain pipes are the simplest option for this drainage.
Water downstream of these outflows will be discolored, indicating its polluted nature. Water pollution and its sources are also viewable in the same info view as for ground pollution. A poorly-positioned pumping station can pump polluted water back into the water supply network, which will make cims sick city-wide. It, therefore, is very important to place drainage pipes downstream of the pump stations.
The water treatment plants function similarly to water drain pipes, but eliminate 85% of the pollution from the sewage prior to disposal. This means there is still a small amount of pollution in the water, and this water should not be used as a source because it can still make citizens sick.
A Floating Garbage Collector filters pollution out of bodies of water. In flowing rivers or other streams, the garbage collector will filter any water that passes over it.
Building pipes under a polluted area has no detrimental effect to the health of a cities citizens.
Traffic, industry, commercial zones, and various buildings (such as power plants and unique buildings) cause noise pollution. When placing a building that produces noise, a circle appears showing the area which will be affected by it. On roads, a general rule is "the heavier the traffic, the heavier the noise". Each type of vehicle has a noise pollution rating, so the amount of traffic noise is dependent not only on how much traffic is present on the road, but also on what types of vehicles are present. Large trucks will typically create more noise, while electric cars tend to be fairly quiet. Policies to encourage electric cars or restrict large vehicles can help reduce traffic noise. Biofuel buses have a lower noise rating than standard buses.
Roads with trees and highways with sound barriers will help to reduce noise produced by vehicles. Noise generated by vehicles of roads under the ground will also be completely suppressed. However, elevated roads will increase noise pollution.
This pollution can be seen graphically on the noise pollution info view, which shows both the emitters of noise pollution and the areas most impacted by it. A high level of noise pollution reduces the land value and citizen happiness. Citizens exposed to the most severe noise pollution will get sick and eventually die if noise pollution persists in the area.
Trees will reduce noise pollution, but must be used in large numbers to see a significant effect.
Citizens affected by any form of pollution will be unhappy and often ill. Pollution also lowers land value around the area. Sound pollution produced by roads can be lowered by upgrading them: sound barriers for motorways, and trees for normal roads. Placing offices will reduce the amount of sound pollution. Buildings producing noise or ground pollution should be in a separate area than residential areas, as residential is negatively affected the most.
- Forum: Parklife Dev Diary #4: Maps and tree noise reduction - CO Emmi (Colossal Order), 2018-05-15