Waterfall Model in Software Testing: Phases, Examples, Advantages & Limitations

The classical waterfall model is the old-school approach to software development that’s all about structure and planning. It helps you map out your entire project from start to finish before writing a single line of code. 

You move through six phases sequentially: requirements, design, development, testing, deployment, and maintenance – without looking back. It’s perfect when you know exactly what you’re building and need solid documentation, especially for government or healthcare projects. 

The downside? It’s pretty rigid, so if requirements change or you find bugs late, you’re in for expensive fixes. That’s why many teams now prefer agile, but waterfall still delivers results and can be combined with other approaches for better outcomes.

When building a home, we usually follow a logical sequence. It starts with blueprints, getting approvals, laying the foundation, and then moving on to walls, roofing and interior. You can’t start with windows before having walls or even a foundation. 

This is exactly how the waterfall model is designed and operates. 

An old-school approach to software development lifecycle (SDLC), the waterfall is all about planning, predictability, and sequencing. Each phase must be completed before moving to the next, creating a structured path from concept to completion.

In this article, you’ll learn everything about the waterfall model, from its phases to its use cases, plus you will find a checklist for using it effectively. 

What is the Waterfall Model?

The waterfall model is a sequential approach to the software development lifecyle where each phase must be completed before moving to the next. Each phase has clearly defined objectives that, once ticked off, teams usually don’t revisit. 

But why the name “waterfall”? Just as water flows in one direction without turning back, the process moves through planning, design, implementation, testing, and maintenance in a strict, linear fashion.

Ironically, Dr. Winston W. Royce introduced this concept in 1970, but as a flawed example rather than a recommendation. Despite that, it became the first widely adopted structured methodology in software development history.

Waterfall still stands out for its straightforward, predictable nature that ensures reliable outcomes. It’s particularly well-suited for projects with well-defined, stable requirements because all planning happens upfront, reducing the risk of costly mid-project changes.

Although newer methodologies have gained popularity in recent years, many teams still use waterfall for projects where predictability matters more than adaptability. Check out how waterfall compares with agile to better understand which approach fits your needs. 

6 Phases of the Waterfall Model You Must Know About 

The classical waterfall model breaks down software development into six distinct, sequential phases. Teams move through each phase one by one, completing all work before advancing to the next stage.

Here are the different phases of the waterfall model:

1. Requirement Gathering and Analysis 

The waterfall model kicks off with collecting and documenting all requirements. For that, the development team collaborates with QA teams, managers, and stakeholders to understand user needs, examine existing systems, and craft a comprehensive software requirements specification (SRS) document. 

Together, they also define project scope, team roles, acceptance criteria, and timelines. This foundational phase maps out what the journey ahead looks like and guides every subsequent decision in the project.

2. System-Design 

With requirements in hand, architects and designers now turn these needs into technical specifications in two ways. First, they define high-level design that outlines the overall system architecture and core components. Followed by the detailed specifications for modules, interfaces, and data structures.

At this stage, the team also establishes testing criteria that will later verify if the implemented system meets the original requirements.

3. Development 

Now comes one of the vital waterfall model phases, which is building. Developers write code based on the design documents, turning plans into working software through programming, unit testing, and code reviews. 

During this stage, they typically work on isolated modules before bringing everything together, carefully following the design standards established earlier.

4. Testing 

After developers complete coding, QA teams step in to verify that the system actually delivers what was promised in the requirements. They follow a structured development testing hierarchy starting with:

• Unit testing: Checking individual components in isolation to ensure they work correctly
• Integration testing: Verifying that different modules work together as expected
• System testing: Evaluating the entire system’s functionality against requirements
• User acceptance testing (UAT): Letting actual users try the system to confirm it meets their needs

What makes this phase particularly critical in the waterfall is that it’s the last chance to catch issues before deployment. There’s no turning back for major changes once you deploy the tool.

5. Deployment 

With testing complete, the software is ready to roll out into the real world. This stage involves preparing installation packages and moving the solution to production environments. The deployment team also creates backup plans and rollback procedures in case unexpected issues arise. 

Additionally, there’s a strong focus on helping end-users transition smoothly by offering comprehensive training sessions and detailed documentation. The goal is not just technical implementation but ensuring actual adoption and proper use of the new system.

6. Maintenance/support 

Probably one of the longest waterfall model phases, it begins after deployment and continues until the software’s retirement. Under this, the focus is on three kinds of maintenance:

• Corrective maintenance: Fixing bugs and defects discovered after deployment
• Adaptive maintenance: Modifying the system to work in changing environments (like new OS versions or regulations)
• Perfective maintenance: Implementing enhancements and new features requested by users

Waterfall Model Example: How it Works in the Real World?

Here’s a waterfall model example using an online banking system as a reference.

1. Requirements 

It starts with the bank meeting customers, managers, and compliance teams to understand what the system needs. Next, they document everything: customers want transfers, balance checks, and bill payments, while regulators require PCI-DSS compliance.

2. System Design 

With requirements in hand, architects plan the system with separate modules for login, accounts, and payments. Plus, all technical specifications get documented before coding starts.

3. Development 

Once designs are finalized, developers build each module step by step, starting with login, then account management, followed by transfer features. 

4. Testing 

After development wraps up, QA teams test individual functions, then check that all parts work together when processing transfers. When that’s done, bank employees try the system for a month using test accounts to ensure it meets daily banking needs.

5. Deployment 

With testing complete, the system goes live during a weekend maintenance window. Customer data moves from the old system, staff get trained, and technical support is offered to help customers with new features.

6. Maintenance 

Finally, the team adds new features like mobile deposits, updates security for new regulations, and fixes bugs as needed. This ongoing support continues throughout the system’s lifetime.

6 Advantages and Disadvantages of the Waterfall Model 

While waterfall offers more reliability and better planning, its rigidity can also create challenges when market and customer preferences keep changing. Understanding these pros and cons can help teams select the right method for their specific project needs.

Advantages of the Waterfall Model That Make it Still Worth

1. Clear structure: The sequenced phases offer a straightforward roadmap that’s easy for everyone to understand and follow.
2. Thorough documentation: Each phase produces comprehensive documentation, creating a valuable knowledge base for future maintenance and enhancements.
3. Early planning: The extensive upfront planning minimizes surprises later in development, potentially reducing costly mid-project changes.
4. Defined milestones: Each phase has specific deliverables and approvals, making it easier to measure progress and keep the project on schedule.
5. Well-planned testing: The dedicated testing phase after development ensures thorough quality assurance before deployment.
6. Easier resource allocation: The clear separation of phases makes budget and resource planning more precise, as costs and tools required can be estimated for each distinct stage of the project.

Disadvantages of the Waterfall Model to Keep in Mind 

1. Inflexible to changes: Once a phase is completed, it’s difficult and costly to go back and incorporate changes or new requirements.
2. Delayed testing: Testing occurs late in the process, which can lead to the discovery of serious issues when they’re most expensive to fix.
3. Client feedback delays: Customers typically don’t see working software until it’s too late, risking misalignment with actual needs.
4. High documentation overhead: The extensive documentation requirements can be time-consuming and delay actual development work.
5. Risk accumulation: Problems often remain hidden until integration or testing phases, creating potential for project delays or failure.
6. Unsuitable for complex projects: Projects with uncertain or evolving requirements struggle under the waterfall’s rigid structure.

Software Testing Using the Classical Waterfall Model 

In the waterfall model, testing stands as its own phase after development. This approach ensures QA activities happen in a structured way, where the completed software is thoroughly checked against what was originally requested.

Here’s how the waterfall model in testing works:

• Test planning: Right from the early stages, QA teams start creating test plans based on the requirements document. They’re essentially mapping out their testing strategy while developers are still busy designing the system.
• Test case development: QA engineers then write detailed test cases that cover every requirement in the spec. They use a requirements traceability matrix (RTM) to make sure nothing gets missed. It’s like a checklist connecting each requirement to the tests that will verify it.
• Test execution sequence: When it’s finally time to test, the team follows a step-by-step approach. They start with unit testing on individual components, move to integration testing, then system testing on the whole application, and finally let real users try it out in UAT.
• Defect management: As testers find bugs, they document everything in a defect tracking system. Each issue gets a severity level and priority rating, and follows a clear path from discovery to resolution.

While this organized approach has its benefits, it also creates some real challenges. With classical waterfall testing, you often find problems late in the game that are costly to fix and might throw off the entire project schedule. 

Plus, if requirements change midway through development, all those carefully crafted test cases need updating too.

When to Use the SDLC Waterfall Model? 4 Popular Use-Cases 

The waterfall model works best when your requirements are crystal clear from the start. It’s meant for environments where changes are minimal and documentation matters. 

Take a look at some of the SDLC waterfall model’s use cases:

1. Government projects 

Waterfall works perfectly for government contracts where requirements are locked in stone. These projects demand extensive documentation, audit trails, and predictable deliverables, which the waterfall model SDLC offers. 

Moreover, changes mid-project can hurt compliance, which is where waterfall rigidity serves as an advantage rather than a limitation.

2. Regulatory projects 

Financial and healthcare software must meet strict regulatory standards like SOX, HIPAA, or FDA requirements. Waterfall’s documentation-heavy approach creates the paper trail regulators demand. Every phase produces artifacts that prove compliance, making audits easier. 

3. Embedded systems 

Embedded systems are specialized software that controls hardware devices like medical equipment or automotive systems. These projects require complete specifications up front and cannot afford to make changes in later stages. 

With the waterfall thorough planning phase, you can ensure all requirements are defined before development, avoiding expensive hardware updates later.

4. Legacy systems maintenance 

Legacy systems are older software applications that businesses still rely on but are difficult to modify. Waterfall works well here because these systems have complex interdependencies that need careful mapping before any changes. 

So, the waterfall model helps in understanding these existing relationships and prevents breaking critical functionality during updates.

4 Well-Known Alternatives to the Classic Waterfall Model to Check out

Beyond the waterfall model, there are also other approaches available in testing and SDLC. Each of these has its strengths and can be a better fit depending on what you’re building and how your team likes to work.

1. Agile: It breaks development into short “sprints” of 2-4 weeks, delivering working software after each cycle. Testing happens throughout, and customer feedback shapes the product as it develops. With that said, agile model values teamwork, adaptability, and meeting user needs over following rigid procedures.
2. DevOps: By bringing together development and operations, DevOps creates a smoother path from code to customer. It relies on automation testing, enabling faster, more reliable releases while making everyone responsible for quality.
3. Spiral model: This risk-driven approach combines elements of both waterfall and iterative development. Projects move through four phases (planning, risk analysis, engineering, and evaluation) in repeated cycles. Its strength lies in early risk identification and mitigation through prototyping.
4. Incremental model: It breaks down a large project into smaller, easier-to-handle pieces that are built and completed one at a time. Each piece follows a complete development process from start to finish. The key benefit is that you get a working product early on that users can actually use, even while you’re still building additional features and improvements.

How to Implement the Waterfall Model? a Quick Checklist for Success

Waterfall has a reputation for being fixed, but it can deliver excellent results when executed properly. The trick is following certain practices that minimize common pitfalls like scope creep and late-stage defects.

Here’s a checklist that combines those practices and serves as your roadmap to success:

Planning and requirements

☐ Requirements fully documented and formally signed off before design starts

☐ Non-functional requirements included (performance, security, compliance, usability)

☐ Dependencies mapped to avoid bottlenecks and missed handoffs

☐ Timelines set with realistic estimates and buffer time, especially for testing

Stakeholder management

☐ Formal sign-offs obtained at every phase to prevent scope creep

☐ Phase-gate reviews scheduled with clear entry/exit criteria

☐ Change control process established with impact assessment steps

☐ Communication plan in place so all stakeholders stay aligned

Risk and quality

☐ High-risk components identified early with mitigation or fallback plans

☐ Acceptance criteria defined upfront for each deliverable

☐ Test strategy and test cases designed during the design phase

☐ Peer reviews conducted for requirements, design, code, and test plans

☐ Traceability matrix maintained to link requirements → design → test cases

Deployment and maintenance

☐ Deployment plan finalized with rollback and recovery procedures

☐ User training, manuals, and support documentation delivered

☐ Maintenance and change request process established post-deployment

☐ Post-project review completed with lessons learned and improvement actions

Final Words on the Classical Waterfall Model 

Waterfall offers structure and documentation that work pretty well for stable projects, especially in regulated industries. 

But today’s market moves fast, and adaptability is key – which is where it can struggle. That’s why many teams are turning to agile and DevOps, which offer the flexibility to adapt quickly through iterative cycles and continuous feedback for faster delivery.

However, you can also mix and match these methods, picking the best elements from each. Your best approach ultimately will depend on your specific project needs.

Whatever path you take, solid testing is essential. With Testsigma, you secure faster testing, better traceability, and fewer last-minute surprises for your projects. It fits perfectly with your waterfall model, turning requirements into automated testing with plain English tests and AI agents. 

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