Can Underground Bunkers Flood?

Yes, underground bunkers can flood if there is water leaking into any of the rooms. When constructing an underground bunker, you should keep water out by determining where it could enter the structure and reinforcing the areas.

At the end of the day, a bunker should protect you from various threats, among which are flooding, environmental contamination from bombs, and biological warfare, among others.

In this article, I will look at what causes the bunker to flood and what you can do about it during construction and renovations.

How Does an Outdoor Bunker Flood?

An underground bunker can flood from ground runoff or from underground.

Every bunker has an over-the-ground access point and inlets to bring air into the living quarters.

These inlets should be constructed high above the surface if on a flat surface.

Otherwise, they should be located on a surface that has a gradient that slopes away from the entrance.

This way, water will never find its way into the bunker.

On the other hand, the bunker may leak water if it sits on the water table.

With time, water may degrade the concrete surface and gain entry into the bunker.

This may take time, but it will eventually happen to your bunker.

Before then, your bunker may get cold and dumpy, which may affect the quality of the air inside it.

How to Prevent Water from Flooding the Underground Bunker

Raise or Relocate the Inlet

If you have built your underground bunker on flat ground, you may consider raising the access points to prevent water entry.

The height at which you will raise the access point depends on the worst-case scenario of flooding.

You can check the flooding predictions for your location to determine the worst-case scenario.

This information is readily available on many government websites for free.

On the other hand, you may relocate the inlet to a location where the land has slanted away.

Beware that this option may be quite expensive as it involves a huge amount of excavation and construction work.

Create a Drainage System

You can also create a drainage system on the surface to guide the water away from the entrance or inlets.

You can excavate the area to create a lasting drainage solution.

However, this is dependent on your budget, the local darainage laws, and the size of your land.

Most people can create smaller drainage systems to connect with the existing system to deal with surface water.

Create an In-Bunker Water Management System

An in-bunker water management system is a secondary system to deal with surface run-off, especially if you live in a flood-prone area.

This system includes a water collection platform that drains water out of the bunker through outlets dug into the side of the structure.

Other systems have extendable inlet and outlet vents that may drain away any flood water beyond a particular height.

In essence, it prevents water from getting into the living spaces and other compartments of the bunker.

Extra Reinforcement

If you are constructing a bunker in a location where the water table is high, you may consider extra reinforcement and waterproofing to keep your bunker sound for a long time.

Consider hiring a professional construction contractor to handle the concrete mixing and reinforcement of your bunker.

Otherwise, try constructing the bunker at a height where it will not come into contact with the underground water.

Construct Your Bunker on the Surface and Bury It

Sometimes it is not possible to have an underground bunker due to the water table and risk of surface flooding.

In such a case, you may consider constructing your bunker partially underground or on the surface and burying it.

Unfortunately, this may require significant amounts of soil or excavation.

Besides, it may be hard to hide the bunker as an underground one.

One way to deal with these issues is to look for a sloping landscape or hillside and build your bunker there.

This solves the issue of concealing your structure as well as surface runoff getting into the structure.


It is possible for an underground bunker to flood.

This may be caused by either of the following:

  • Surface run-off that gets into the bunker via the access points and air inlets
  • Underground water that gets into the bunker via the floor and walls

You can deal with the problem by doing the following:

  • Raise or Relocate the Inlet
  • Create a drainage system on the surface.
  • Create an in-bunker water management system or extendable water management inlets and outlets.
  • Reinforce and waterproof your bunker against underground water.
  • Construct your bunker on the surface and bury it.

The best solution depends on the source of the threat of flooding and its extent.

If you have various options, consider trying the cheapest option first to save on cash.

You should also check if your area has a risk of flooding and how high the water table is before constructing an underground bunker.