Rainfall brings simulation depth and new gameplay elements to the primarily cosmetic game concept of dynamic weather that was introduced with Snowfall. When the game is raining, this mod adds a water sources in a grid over a selections of tiles specified in your options up to 25 tiles. You must create and manage a storm drain network in order to protect your city from suffering the effects of flooding. You should be aware of and plan out the grading of any zoned roadways and add storm drain inlets to any low points in the roads. Options for Storm Water Management include surface ponds, underground detention systems, canals, and riverine channels.

All storm drain assets must be connected to your sewer and water system but only use 1 water and 1 sewer. They do not dump sewage produced by buildings, however they may transport or simulate polluted water. It does not contribute to the water or sewage because storm drain water is kept separate.

The types of storm drain assets are inlets, outlets, detention basins, and pumps.

Storm Drain Inlets and Pumps direct any storm water that is collected to Underground Detention Basins within the same district first, and then to Gravity Storm Drain Outlets and SD Force Main Outlets in the same district once the Detention Basins have reached 80% filled. Anything not included in a district is actually in District 0. You cannot actually draw storm drain pipes, but all storm drain assets must be connected to your sewer and water system. They only require 1 water and 1 sewage. They do not contribute to the water or sewage because storm drain water is kept separate.

The Storm Drain Assets by themselves can be used to transport water throughout your city. You may even elect to turn the Storm Water Difficulty down to 0 so that you don't have to deal with stormwater, but can still use these assets to move water around your city or clean up after damming mistakes and demolished canals.

See Rainfall Collection for links to the assets.

The official rainfall inlet assets include the standalone inlet, and various pairs of inlets at different widths. These assets collect storm water, but all require gravity flow to carry that water to the outlet. They do not require nor conduct electricity. You need to build inlets at all low points in your development and you may also need them periodically along long sloped roads to prevent the water in the streets from flooding nearby buildings.

The new props can be difficult to see with certain pavement colors I recommend
Roads United: Core+ and altering the brightness of the pavement so that you can see the decals. I thought these decals where an improvement over the old props because the decals follow the surface of the road rather than hovering over it. Anarchy is recommended for placing on top of roads but The Move It! mod with Snapping options allows for inlets to be perfectly snapped onto roads. That method does not require anarchy.

If you want the old props just edit your copy of the assets.

The official Rainfall outlet assets include the bubble up outlet, gravity storm drain outlet, force main outlet, canal outlet, gravity outlet with filter, and force main outlet with filter. These assets release storm water that was collected by inlet assets. Most require gravity flow, but the force main outlets do not.

Outlet assets must be connected to your sewer and water system but only uses 1 water and 1 sewer. They do not dump sewage created by buildings, however they may transmit or release polluted water. It does not contribute to the water or sewage of your city because storm drain water is kept separate.

By default the canal outlet, gravity storm drain outlet, and force main outlet snap to shore lines and canals. By default the outlets with filters are placed roadside.
If you hold ALT while placing one then you can place it anywhere.

You can change the elevation of an outlet by selecting it and pressing Page Up/Page Down. A connected water pipe will need to be reconnected before the outlet will work again. You can also use the Move It! mod which can also move the connected water pipe simultaneously. The canal outlet, and bubble up outlet will not visually move, but the variables for elevation will change using Page Up/Page Down or Move It!. To better manipulate those assets you should use landscaping tools and manual relocation.

Except for problems related to sewer, water, or electrical connections ignore what the problem actually says, and look at the text under the description of the asset when you select it.

Line Not Connected - You don't have any outlets/detention basins in the same district. Add an outlet/detention basin in this district or move the inlet to another district with an outlet/detention basin. You can also turn off district control in the option menu.

Landfill Full - There is not enough outlet/detention capacity within this district. Build additional outlets/detention basins or wait for the storm to lessen.

No Place For Goods - Cannot gravity drain to outlet. You must either build a lower gravity storm drain outlet, a detention basin, or a SD Force Main outlet. You can also turn off gravity flow in the options menu.

Line Not Connected - You don't have any inlets in the same district. Add an inlet in this district or move the outlet to another district with an inlet. You can also turn off district control in the option menu.

Landfill Full - There is not enough outlet capacity within this district. Build additional outlets or wait for the storm to lessen.

Flooding - The water surface elevation is above the invert of the outlet. The outlet will continue to function but at a reduced rate. This rate will continue to drop as the water surface elevation rises to the soffit of the outlet. This will only happen with the Improved (Beta) Gravity mechanics option.

Flooded - The water surface elevation is above the soffit of the outlet. The outlet will continue to function but at the minimum (25%) rate. This will only happen with the Improved (Beta) Gravity mechanics option.


Line Not Connected - You don't have any inlets in the same district. Add an inlet in this district or move the basin to another district with an inlet. You can also turn off district control in the option menu.

Landfill Full - The detention basin is full. The basin will slowly drain at the infiltration rate. You can Turn Off the detention basin and no more water will flow to it if you want to drain it more quickly.

Storm Drain Inlets and Pumps direct any storm water that is collected to Underground Detention Basins within the same district first, and then to Gravity Storm Drain Outlets and SD Force Main Outlets in the same district once the Detention Basins have reached 80% filled. Anything not included in a district is actually in District 0.

District control for the storm drain assets allows you to direct which inlets and pumps drain to which outlets and/or detention basin. This allows you to simulate drainage districts that flow to specific ponds, canals, etc. If you want to drain a section of water into a dry basin then you can control that by putting the inlet or pump within the same district as the outlet. The problems you may encounter with this is that you may need to design your districts in order to accommodate having their own outlets. The easiest way to accommodate this is by utilizing canals or drainage ditches and having districts on either side of it with at least one outlet per district. Another method is to have a pond with at least one outlet and and an inlet that is not in any district (district 0) which will connect the pond to another outlet downstream.

Storm Drain Inlets and Pumps direct any storm water that is collected to Underground Detention Basins first, and then to Storm Drain Outlets once the Detention Basins have reached 80% filled.

Having district control off simplifies the storm drain system down to about the same level as a standard cities skylines service. All inlets and pumps are connected to all outlets and detention basins. The problem you may encounter with this is that you cannot control which outlet water will come out from once it enters an inlet.

Allows you to connect storm drain assets into groups based off a common building id that you can set when you click on each asset and change its name. The default names cannot be used as group names for that asset.

This combines the best aspects of the two systems. It uses ID control whenever the name of the asset does not match the default, and district control when the name is the default.

There are three settings for gravity drainage mechanics: Ignore Gravity, Simplified (Alpha) Mechanics, Improved (Beta) Mechanics.

This allows you to avoid ever having to deal with the problem that your inlets cannot drain to your outlet. This is basically cheating though, to be fair you should just utilize force main outlets and pay the premium for ignoring the effects of gravity.

This was the simple method for determining gravity drainage that came with the alpha version of the mod. The inlets can drain to the gravity outlet as long as the elevation of the inlet is higher than the elevation of the outlet. The elevations are based on the insertion elevation, which is at the bottom of the asset.

The improved method came with the Beta version of the mod. In order to determine if the inlet can drain to the outlet, the higher of the Inlet Elevation and the water surface elevation at the inlet must be greater than the higher of outlet invert and the water surface elevation at the outlet. This allows the mod to represent a basic concept of fluid mechanics which is static equilibrium. Outlets will also flow at reduced capacities once the water surface elevation rises above the invert. Outlets flow will reduced to a minimum of 25% once the water surface elevation rises above the soffit of the outlet.

Requires Improved (Beta) Mechanics and prevents inlets from working when the water surface elevation is below the rim of the inlet.

Detains stormwater underground which slowly infiltrates into the ground. It is still important to have an outlet within the same district in case the basin fills completely.

I recommend using some form of anarchy to place within a park.

Underground detention systems must be empty before you can relocate/demolish them. Turning them off will prevent any more water from flowing to one.

Underground detention systems by default can only be placed on the ground above water.
If you hold ALT then you can place them underwater. . . if you wanted to for some reason.

ms6615 pointed out on reddit that this can be used to create a septic/leech field to infiltrate polluted sewage water into the ground.

Pumps storm water into storm drain system. Does not require gravity flow but requires electricity. This asset is mainly used to move water around your city.
I don't recommend keeping a storm drain pump and an underground detention basin in the same district unless you're intentionally trying to remove water from your city permanently.

Flood spawning assets are not compatible with the current version of Rainfall. They will be implemented in a future update.


The Retention Basin assets are free, no maintenance, and can be placed anywhere. They will spawn water to represent ground water up to the depth in the title. The are perfect for creating ponds and lakes in your city and will rise and fall with incoming storm water when using Rainfall.

It is very important that the water can reach the depth of the "ground water" because the asset will continue to produce water at increasing rates until it does. Make sure you built the bowl of the lake before you put the asset into it.

You should be able to alter the height of the ground water with Page Up/Page Down. The water rises much faster than it falls.

These are very helpful in alleviating Land Value Spikes which is an inherent issue with the Rainfall Mod.

Stormwater pollution will be added back into rainfall in a future update.

Some outlets can have filters built into the outlet. They are more expensive to built and maintain, however they do not produce pollution. Instead, they produce garbage and must have road access in order for the garbage trucks to access the filter.

Without stormwater pollution, these aren't actually necessary.

#RainForecast Chirps: At the beginning of a non-vanilla storm simulation you will get a chirp with data about the upcoming storm event.
#Rainfall Chirps: Random chirps that relate to the current intensity of the storm
Prevent Rain Before Milestone: Turns on or off whether the mod prevents rain from happening before you reach the milestone where the basic storm drain assets are unlocked.
Prevent Building Upgrades from Increased Landvalue due to Rainwater: Turns this feature on or off. This does not help with water than remains or is still flowing once it stops raining. I recommend utilizing retention ponds with a ground water asset which always have some water in them.
Previous Storm Options: Options on how to handle loading a game that is already raining.
Building/Roadway Flooding/Flooded Tolerance: Allows you to change the amount of water depth required to causes problems to occur in Buildings and Roadways.

Although it is unrealistic, the easiest way to setup your water network is to be create a grid that is half way between your streets. This will make it easy to place your inlets on top of the streets using anarchy and then connect pipe laterals from the inlets to the main.

1. Start a new city and design it to handle the changes from this mod. If you insist on using this with an existing city, then make a copy first.
2. Keep your road profiles below existing grade to encourage water to drain to the streets.
3. Undulate roads with high and low points and put inlets at any low points.
4. Build your inlets at the low points in your development before drawing the water pipes. The Inlets generally want to snap to water pipes and it can be pretty annoying.
5. A Detention Pond should always have an outlet. . . unless you can guarantee that it can handle the largest storm possible.
6. Keep your polluted storm water away from Drinking Water Intakes. (I learned that the hard way)
7. If a district is not adjacent to a river, canal, or other water feature, you can create a pond and have an inlet in/near the pond that is in District 0 that gets the water from the pond to the next water feature.
8. Building in the rain can be difficult (Yay for realism!). Fine Road Anarchy will help you place important buildings, and roads while it is raining.
9. Move It! mod can raise and lower any building including zoned buildings. I recommend utilizing that to help those pesky zoned buildings that don't seem like they shouldn't be flooding but say that they are flooding.

BloodyPenguin, Snow_Cat, SamsamTS, Overhatted, Runaurufu, Soldyne, NS5 X, PropaneDragon, Simie, Soda & emf. Your mods helped create this one, either by your open source code or using the mods you've created. Thanks.

First off let me say that Rainfall doesn't alter your savefile in any abnormal way. However water and water sources are saved into your save file with the vanilla game so if you use rainfall to put a bunch of water sources into your city, flood your city, save, and remove rainfall then their is no way for rainfall to remove those water sources or the water. Follow these steps to safely remove rainfall before you remove the mod.


1. Click "End Storm" button in the in-game option menu.
2. Set "Global Runoff Scalar" to 0.
3. Remove any storm water using inlets and pumps as necessary.
4. Remove all rainfall assets. Storm drain assets can be removed with the "Delete Rainfall Assets" button in the in-game options menu.
5. Click "Terminate" button in the in-game option menu.
6. Save and return to the main menu.
7. Remove Rainfall Mod in the content menu.
8. Restart Cities Skylines.