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, however; the farming and forestry industry specializations don't cause ground pollution while the other specializations increase it. It is also caused by other polluting buildings, such as fossil-fuel power stations, airports, 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.
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 these buildings, instead it is transported through your pipes 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 discoloured, indicating its polluted nature. Water pollution and its sources are also viewable in the same info view as for ground pollution. A poorly-position pumping station can pump polluted water back into the water supply network, which will make cims sick city-wide. It is therefore very important to place pumping stations upstream of the drainage.
Water treatment plants function similarly to water drain pipes, but eliminate most of the pollution from the sewage prior to disposal.
Building pipes under a polluted area has no detrimental effect.
Roads, industry, commercial zones, and various buildings (such as power plants and unique buildings) cause sound pollution. When placing a noisy building, a circle will appear showing the area which will be affected by the noise.
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 this.
A high level of noise pollution reduces land value and citizen happiness. Citizens exposed to the most severe noise pollution will get sick. Lining roads with trees reduces their noise impact, as does erecting barriers on highways.
Citizens don't like to live near pollution. It makes them unhappy and decreases their health, it also lowers land value around polluted land. Pollution can no longer be decreased by planting trees in polluted areas. 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 moved away from residential areas.