What Is the Waterfall Model in Software Engineering? A Complete Guide

The Waterfall project methodology is one of the oldest and most structured ways of implementing a new project and has been routinely utilized throughout the evolution of Project Programming, and remains widely used by many sectors to this day.

For example, the Waterfall project methodology is ideal in situations where there are relatively few unknown requirements within the project and the requirements are unlikely to change; therefore, it provides an excellent structure that avoids confusion upon completion.

The Waterfall project methodology provides excellent support for teams by offering a clearly defined plan for completing the project; all team members know exactly what to do throughout the process and have a clear path to follow. 

As an individual, whether a student or someone interested in a career in software development, it is vital to understand how projects were traditionally built using the Waterfall methodology and how it is still widely used in some industries.

What Is Waterfall Model In Software Engineering?

A Waterfall Model is a phased approach to software product development that requires completion of each phase before advancing to the next. Once the water flows past each step, it cannot return to that step.

The Waterfall Model begins with requirements gathering (clarification) through understanding the customer's vision, followed by system design, system build, system testing, and finally system delivery to the customer. 

Due to the linear flow of the Waterfall Model, it is most effective for projects with well-defined needs and/or a small number of anticipated changes.

The Waterfall Model is straightforward, with predictable timelines, a clear path, and a structured approach to Product Development. 

A significant disadvantage of the Waterfall Model is that it does not support changes after the Testing phase; thus, it is difficult to modify the system once it has been tested and put into operational use.

What Is the Waterfall Process Model In Software Engineering?

Waterfall is a sequential, or linear, method of software development. Each phase in the Waterfall process is completed prior to beginning the next phase; thus, the flow of the project resembles that of water as it cascades down a series of stair steps.

In general, once you complete all tasks in a phase, you cannot return to that phase unless there has been a significant change in project requirements. 

As a result, Waterfall works best with software projects that have clear requirements and specifications at the start of development.

Due to the fact that Waterfall provides a consistent development structure, supports comprehensive documentation, and offers predictability with respect to completion timelines, the Waterfall process is a popular choice for the majority of today's traditional software projects.

The following provides detailed descriptions of all phases associated with the Waterfall model:

1. Requirements Gathering

The requirements gathering phase serves as the foundation upon which the rest of the project will be built.

During this phase, we gather all necessary details regarding exactly what the customer expects from the Software Application, including:

All features, functions, user needs, etc. will be documented clearly in the final SRS document.

This is strictly a research phase; no coding or designing occurs during this phase.

It is important to note that the SRS document will serve as the primary reference document for the remaining segments of a project.

2. Design Phase

During the design phase of the cycle, the development team will translate the requirements into a blueprint of how the application will operate.  

There are two steps to this process: 

1. The high-level design (HLD) outlines the architecture of the application and determines which tools and technologies will be used to build it. It includes how data will move through the application and what type of app will be created.  

2. The low-level design (LLD) provides detailed technical information about how to implement each feature, including how to store data, the application interface (API), user interface (UI), etc. 

With the high-level and low-level designs complete, developers can begin building the application. 

For example, when creating the hotel's booking system, the HLD would outline how the database will be structured, which programming languages to use, and examples of how the UI will look. The LLD would provide specifics on how the booking logic will be performed, as well as how to store and retrieve reservation data.

3. Code Implementation Phase

The development process starts with this phase.

The designers supply the developers with their design specifications from which the software is created through coding.

Each software component is developed as an independent module before the complete application is built by integrating and testing the modules together.

The primary concern in this phase is writing clean, functional, and practical programs that meet the specifications.

Because the Waterfall model lacks flexibility, developers will work within the specifications established by the designers.

4. Verification

The verification (testing) phase begins once coding is complete. All software components must be thoroughly examined.

Testers will review all aspects of the application to determine whether it meets the requirements defined in the SRS. 

Testers may conduct various forms of functional testing, as well as integration testing, system testing, and acceptance testing by end users of the application. 

Any defects discovered during testing will be documented, but they must be addressed before being retested.

The major objective of this phase is to produce a reliable, stable product. 

5. Maintenance Phase 

Continuing the Software Development Life Cycle -- Maintenance Phase (SDELC)

Real Users Will Begin Using the Software After the Software Is Released.

When Software Is Made Available, Real Users Will Use The Software Once It's Released.

Any problems discovered after the software is launched will be resolved through fixes.

Software Updates Or Minor Enhancements Can Be Implemented After A Software Release.

If an issue arises, a support solution is available. Perpetual Maintenance Will Keep Software Relevant And Current For Many Years.

What Are The Types Of Waterfall Model In Software Engineering?

The four commonly recognized types of waterfall model in software engineering are the Classical Waterfall, Iterative Waterfall, the Sashimi (Overlapping) Waterfall, and the V-Model. Each one takes the core idea of Waterfall, moving through phases in order, but adapts it to fit real project challenges better.

1. The Classical Waterfall Model 

It is the first and the most structured model there is. Each step has to be completely finished before the team moves to the next step. 

There will be no overlap between phases. There will be no 'go back' after a phase is finished.

The Classical Waterfall Model is suited for projects where the specific requirements are understood and will not change during the project cycle. 

The Classical Waterfall Model approaches the project in a linear way. The specific steps that make up this model are: Requirements, Design, Implementation, Testing, Deployment, and Maintenance. 

A major benefit of this model is that it establishes excellent levels of documentation, predictable timelines, and a disciplined approach to development. 

A major disadvantage to this model is that once approved it is difficult for the team to fix mistakes that might occur at a later date.

2. The Iterative Waterfall Model 

It follows all the same steps as the Classical Waterfall Model, but offers a bit more flexibility. 

With this model, the team can move backward as many times as needed, and it does not require them to continue forward regardless of the circumstances. 

The Iterative Waterfall Model acknowledges that mistakes can occur and that clarifications may be needed in a project's requirements before moving on to the next phase.

 If any discrepancies are found during the Testing phase, the team can reroute back into the Design or Requirements phase and revise the project accordingly. 

Reiteration reduces risk and helps prevent large-scale failures throughout the project.

3. Sashimi (Overlapping) Waterfall Model

The Sashimi model, also known as the Overlapping Waterfall model, is a variant of the traditional Waterfall model in which phases occur simultaneously rather than sequentially. 

Phases that overlap allow development work to commence before the preceding phase is completed. 

For instance, while some of the detailed requirements are still being established, the design team can initiate draft designs for the system's structure. 

The process of overlapping helps speed up development time, improves communication between team members, and minimizes delivery delays to customers, particularly when teams must work closely together to perform their respective functions. 

The term "Sashimi" is derived from the Japanese dish, which is made from several pieces of fish, sliced and layered on top of one another. Like the term' indication,' the phases in the Sashimi model overlap.

4. V-Shaped Model (V-Model)

The V-Model takes the Waterfall concept one step further by placing equal weight on both the development and the testing process. 

Each phase of the development process represented on the left-hand side of the letter "V" has a corresponding phase of testing on the right-hand side (e.g., requirements and acceptance testing; design and system testing; code and unit testing). 

The V-Model focuses on the quality of the product throughout the entire lifecycle and ensures that quality assurance (QA) activities are done continuously throughout the lifecycle rather than being viewed as a final QA step. 

The V-Model is particularly useful for projects that require repetition of processes or for those in which multiple teams will be working on the same elements concurrently.

What Are The Examples Of Waterfall Models?

Imagine a company wants to build a school management system to handle student records, fees, attendance, and reports. The Waterfall model fits well because the school’s needs are stable and clearly defined.

1. Requirements Phase 

The team meets teachers, admin staff, and school management to gather all requirements. They finalize details like:

• Add and manage student profiles

• Track attendance

• Generate fee receipts

• Create progress reports

• Manage teacher records

All these requirements are documented in an SRS (Software Requirements Specification).

Output: A complete list of features with no missing details.

2. Design Phase

The development team now converts the requirements into a technical plan. They create:

• System architecture (modules like students, attendance, fees)

• Database design (tables for students, teachers, marks, payments)

• UI layouts (login page, dashboard, student list)

• Workflow diagrams (how data moves across modules)

Output: High-Level and Low-Level design documents.

3. Implementation Phase

Developers write the actual code based on the design. Examples of what gets developed:

• Student registration form

• Attendance entry module

• Fee collection and receipt generation

• Report card generation

• Admin login and permissions

Each module is coded separately and then integrated.

Output: Complete working software.

4. Verification (Testing) Phase

The testing team checks whether the system matches the requirements.

They test:

• Can a student be added successfully?

• Are attendance reports accurate?

• Does the system calculate fees correctly?

• Are progress reports generated without errors?

• Can only authorized users log in?

Any bugs found are fixed before final release.

Output: A stable, error-free system ready for use.

5. Maintenance Phase 

Once the school starts using the system, new needs or small issues may appear. Examples of maintenance tasks:

• Adding a new field like “Blood Group” in student profiles

• Fixing slow-loading screens

• Updating the system for the new academic rules

• Providing technical support when teachers face issues

Output: Regular updates and fixes to keep the system efficient.

What are the Features of Waterfall Model?

The main features of the Waterfall model are the Sequential Approach, Document-Driven, Rigorous Planning, and Quality Control. These features work together to create a clear, step-by-step workflow. Let’s discuss them below.

1. Sequential Style, Sequential Flow

The Waterfall methodology uses a sequential process so that no phase starts until the previous one has been completed. Each step provides clear information to the next phase, allowing greater clarity between the customer and the developer.

2. Documentation-Based Model

While each phase generates significant documentation, the use of these documents drives the success of this process. These documents provide the roadmap for the team, clarify the project's end product, and keep the team on track with the goals and objectives.

3. Rigorous Planning Phase

Prior to beginning any development work, the project is thoroughly defined. The project scope, time frames, available resources, and deliverables are all established to ensure that teams remain properly organized throughout the life of the project and that the project does not require significant changes once it has started.

4. Quality Assurance Processes are Conducted at the End of Every Phase

At the end of each phase of development, a review of the product is conducted to identify and correct errors before moving to the next phase. By performing reviews at each phase of development, the finished product can be assured of meeting stakeholder requirements.

What Is the Importance of Using the Waterfall Model?

Before going into the details, it's important to remember why the Waterfall model is still useful in many development settings. 

It is clear and simple, has well-defined phases, strong documentation, stable requirements, makes good use of resources, and is good for smaller projects. Let's take a closer look at each of these points.

1. Transparency and Simplicity

The Waterfall Model's linear pathway provides a transparent approach for teams to know where they stand in their project and to follow through directly. The linearity of the Waterfall Model reduces uncertainty and leads to a more consistent development process.

2. Clearly Defined Steps

The Waterfall Model identifies clearly defined steps for each phase of the project. This clarity of understanding makes it easy for teams to plan and manage progress through the designated checkpoints established for each phase.

3. Documentation

Because the Waterfall Model requires comprehensive documentation for each phase, it makes it easier to understand, maintain, and upgrade the software later.

4. Consistent Requirements

The Waterfall Model works optimally when the project's requirements remain fixed and are not expected to change. Because requirements do not change significantly during the project, the potential for increased rework and uncertainty is minimized.

5. Importantly Utilized Resources

In the Waterfall model, team members/resources are allocated to each phase. Therefore, team members can devote full concentration to the specific functions of that phase without having to change their focus during project development continuously.

6. Utilization of Waterfall for Smaller Projects

The Waterfall Model may be the most efficient and economical way to develop a small project with simple, predictable, and fixed requirements.

Waterfall Model In Software Engineering Advantages And Disadvantages

Before adopting the Waterfall model in your project, you should evaluate where it works best and where it may not work at all. 

The Waterfall model provides many advantages, such as clarity, organization, and well-defined timelines. 

However, it also has limitations when dealing with requirements that change quickly or on complex projects. Let's review the advantages and disadvantages of the Waterfall Method below.

What are the Advantages of Waterfall Model?

The Waterfall model offers many advantages, including clarity, organization, and well-defined timelines etc. Let's discuss them one by one. 

1. Simple to Understand and Manage.

Very straightforward; step-by-step design allows for many teams to handle projects using a sequential method (for teams that want to have more control of their working method).

2. Clearly defined steps.

With clearly defined steps and objectives at every stage of development, this makes it much easier to plan, monitor, and review progress.

3. Extensive Documentation.

Extensive documentation is generated for each phase of the process. When the documentation is generated regularly from the beginning of development, the software will be much easier to maintain; if there are changes in staffing, new employees can be brought in at any time with minimal disruption to the existing team.

4. Predictable Flow of Project Work.

With a fixed timeline, comprehensive requirements, and clearly defined deliverables, stakeholders can expect to be able to clearly assess the progress of the project and expected results throughout development.

5. Great for Requirements that are not Likely to Change.

The Waterfall Model is ideally suited for those situations where the customer knows exactly what they want, and changes are not anticipated during development of the product.

What are the Disadvantages of Waterfall Model

As we have seen, the waterfall model offers many advantages; however, there are a lot of limitations of the waterfall model in software engineering when dealing with requirements that change quickly or on complex projects. 

Let's review the disadvantages of the Waterfall Method below.

1. Rigidness in Flexibility

Once a phase is complete in the Waterfall model, it is hard to go back and modify it. Therefore, this model is not ideal if your requirements are ever-changing.

2. Feedback from Testing Comes Late

In the Waterfall model, testing only takes place after the completion of development, meaning potential defects and problems will not be found until way down the line.

3. Increased Rework Risk

An error made at an earlier stage of a project may require a significant amount of time and money to fix.

4. Less Suitable for Projects Needing Iterative/Creative Development:

The Waterfall model is less suitable for large or complex projects that require constant input, feedback, and creativity.

5. More Difficulty Changing Towards New Conditions

Once you have locked down your plans/requirements early on in your project timeline, you are less able to change them as new information or user needs arise.

When to use the Waterfall Model?

• Appropriate for projects that have clear, stable, and well-defined requirements.

• Best suited for clients who have a clear understanding of what the finished product should look like.

• Small or medium-sized projects that have simple structures are likely to produce the best results.

• An excellent option for teams that are comfortable with a step-by-step approach to development and prefer a fixed flow.

• Ideal for situations that require detailed documentation for maintenance or compliance.

• Valuable for those teams that prefer to work in a linear fashion rather than iteratively.

• Highly effective when a project requires predictable timelines, budgets, and deliverables.

• Applicable in instances where testing of the system will occur after the entire system has been developed.

Final Thoughts

The Waterfall model is a classic method still widely used for software engineering. Its structured flow makes it easy to understand, plan, and develop software projects accurately. 

The Waterfall model is an effective method for developing a project with stable requirements, requiring a high level of detail and tracking in each phase, and supporting a team that desires individual, stepwise progress through multiple stages. 

Although other modern development techniques, such as those based on Agile principles, offer greater flexibility, developers working in environments where documentation, monitoring, and other controls/management are essential will find Waterfall still helpful in tracking their development process. 

Understanding how the Waterfall model has historically been used to develop software will help students, developers, and project development teams understand why many industries still use it today. 

Finally, when appropriately used for a development project, the Waterfall model provides a high level of confidence and consistency, producing high-quality, reliable results.