What are Dependencies?

Dependencies are relationships of reliance within and among infrastructure assets and systems that must be maintained for those systems to operate and provide services. The National Infrastructure Protection Plan affirms that an understanding of critical infrastructure dependencies is essential to enhancing the resilience of communities. Let’s take a look at some of the factors that inform how we think about dependencies.

Dependencies often flow both ways

Image depicting that interruptions to communications and the energy sector can disrupt the other

Dependencies can be one-directional or bi-directional (also known as interdependencies*), and can be upstream or downstream. For example, the energy and water systems are often mutually dependent on each other.

Dependencies are far-reaching

Dependencies can affect multiple jurisdictions simultaneously

Systems, and their dependencies often span across regions and jurisdictional boundaries and addressing them may mean working with regional partners and private sector operators.

Dependencies can have a cascading effect

Dependencies mean that disruptions to one sector may affect others indirectly. For example, disruption to the energy sector can impact communications, which in turn could impact the water sector.

An asset within an infrastructure system goes down causing the entire system to lose function, which impacts another critical infrastructure asset using this downed system’s resources, further impacting the assets and systems that rely on it for operational services.

Dependencies take many forms

Dependencies can be physical, geographic, cyber, or logical in nature.





  • Operations rely on other infrastructure and supply chains to provide services and/or commodities as an input.
  • A water facility relies on chemicals and electricity produced by external providers.


  • Operations rely on information and data produced or managed by others.
  • A fuel terminal relies on IT and communication systems to operate accounting and billing systems to distribute fuel.


  • Operations of multiple systems are collocated and susceptible to similar hazards or a single disruption.
  • Gas, electric, and water lines sharing a right of way can all be disrupted simultaneously.


  • Operations rely on other systems due to economic, policy, or human factors.
  • Travel restrictions enacted in one state may impact cross-state transportation of goods causing supply chain issues or new regulations on the chemical sector may impact the operations of sectors who use chemicals, such as water and food & agriculture.

It is important to note that dependencies extend beyond just physical connections between assets and systems. As illustrated in the graphic below, disruptions to the production or transportation of key products and resources that serve as inputs (such as chlorine for water treatment) can disrupt critical infrastructure operations. These supply chain considerations can be an important part of understanding dependencies that can impact communities.

Communities are reliant on critical infrastructure to deliver all basic societal functions like health, education, and a functional government and economy. Because critical infrastructure assets and systems are dependent on each other to function properly, it is important that communities understand and account for these dependencies.

It’s important to note that infrastructure systems can be owned and operated entirely by one entity or by a number of owners and operators, both public and private, working together to deliver goods and services. Because of this, gaining an understanding of infrastructure systems and dependencies will often mean working with a wide range of partners.

Now that we have a general understanding of dependencies, let’s see how they play out in a simplified example.




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