What is a Waterfall Model in SDLC?


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January 16, 2023

The Waterfall is a project management model co-opted into the software development life cycle (SDLC). It takes a successional approach to software development by splitting projects into independent phases and tackling them one after the other. 


Each phase has its target set, and after its completion, the cycle proceeds. Phases cannot overlap others in the Waterfall model, so progression relies on completing previous phases. 

In addition to that, completed projects cannot be revisited. Major corrections mean the cycle has to be scrapped and restarted. 

Waterfall is the oldest SDLC model and was the basis for developing all the other models. However, its strict rules point to its history of being outside the software industry. An example is that in building a house, you lay the foundation before building the walls. And in the occurrence of a significant flaw in the foundation, it cannot be revisited unless the 

project is collapsed and restarted.  In software development, however, there is leeway in revisiting the coding phase to address minor bugs. 


The waterfall model bases its operations on three core principles:

·      Sequential Structure

·        Robust Documentation 

·        Minimal customer involvement 

Having already discussed the sequential nature of Waterfall, we will quickly look at the other two. 

Robust documentation means the waterfall model emphasises foreplanning and intensive information gathering before the step is taken or code written. 

The waterfall model also limits customer input during the development process, except via controlled experiments during testing. This is because the model’s structure does not allow for flexible iterations, meaning input cannot be easily implemented. 

The Waterfall SDLC model typically flows down through 6 stages. It is visually represented as a literal waterfall running down a slope. The water flows downward step-by-step and cannot flow backwards onto a previous step. 


Stages of Waterfall Model 

They are explained below:


This stage aims to identify and gather all the information relevant to the SDLC. This includes the full specifications of the customer's requirement, feasibility studies and other documentation. These data can be gathered from interviews, questionnaires, and buzz sessions. They analysed for flaws and limitations and then incorporated into a single document called Software Requirements Specification (SRS). 



This phase aims to prepare the gathered document for coding. It is converted into a format that the developers can easily represent with a programming language. Here also,  suitable 

programming languages and other architecture are agreed upon. The outcome of this process is a document known as a Software Design Document(SDD). 

The planning process in the design phase is usually split into two units called logical and physical design.


 ·        Logical design phase formulates and answers theoretical questions that may be encountered in the project. It discusses methods, solutions, principles, techniques and philosophies. 


Physical Design entails the inventory specification required to implemen the discussed solution. It specifies hardware, software, personnel and architecture.


This is where hands-on production begins. By this stage, the developers clearly understand 

what the end product should be. The focus is to bring life to the ideas constructed in the 

SDD through written code. In large-scale or complex projects, the developers may be split 

into smaller teams to work on different units of the project. These units are tested 

independently before they are integrated into the overall SDLC. 



The conclusion of the coding phase means that a product has been built. That product will 

then be rigorously tested to determine its functionality and identify flaws or 'bugs' that 

impede customer requirements or satisfaction. On an enormous scope, this process is 

called Software testing. It is split into functional and non-functional testing. 


Functional: Unit testing, Integration testing, System testing and acceptance testing. 


Non-functional: Security, performance, usability, and compatibility testing. 


Suppose the product passes all of these tests, the SDLC flows on. If it does not, the 

detection of minor flaws will result in a forced repeat of the coding phase. This is the only 

point in the Waterfall model where a revisit is allowed. However, if the flaws in coding are 

major, the entire SDLC will be restarted.  


Sometimes customers can get involved using a User Acceptance Test agreement at this 

stage. This is done to get feedback from the intended user of the product. It aims to 

uncover bugs that have gone unnoticed by the developers because they only surface 

during day-day use. It is the last phase of testing before deployment. 



A product that passes the testing phase is ready for consumption and made available for use by the intended customer. 


This is arguably the most essential part of the SDLC. It is an indefinite process that exists to keep the customer satisfied. It involves corrections, code adaptations & general customer service as required. Maintenance continues until perfection is achieved. 



of Waterfall Model

·        Easy to understand, manage, and use: The Waterfall model is a straightforward and sequential approach to project management, making it easy to understand and use. This can be especially beneficial for teams that are new to agile or project management in general.

·        Enforces structured, disciplined organization: The Waterfall model's linear structure and well-defined phases enforce a structured and disciplined approach to project management. This can help teams to stay on track and avoid scope creep.

·        Detailed documentation and clearly defined steps make it easy to replicate: The Waterfall model's emphasis on documentation and clearly defined steps makes it easy to replicate projects. This can be helpful for teams that need to develop similar products or services repeatedly.

·        Accurate projection of estimated cost and timeline: The Waterfall model's sequential approach and detailed planning make it easier to accurately project the estimated cost and timeline of a project. This can help teams to manage their resources and expectations more effectively.

·        Robust documentation helps point out errors early: The Waterfall model's emphasis on documentation can help to identify and correct errors early on in the project development process. This can save time and money in the long run.

·        Clearly defines milestones and progress due to the structural and planned approach: The Waterfall model's well-defined phases and milestones make it easy to track progress and identify potential problems early on. This can help teams to stay on track and deliver the project on time and within budget.

·        Limited customer input can prevent an overload of suggestions and changes: The Waterfall model's sequential approach and focus on planning can help to limit customer input and prevent scope creep. This can be helpful for projects where the requirements are clearly defined and understood.

·        Detailed, structured, and documented procedures make it easy to replicate: The Waterfall model's emphasis on documentation and structured procedures makes it easy to replicate projects. This can be helpful for teams that need to develop similar products or services repeatedly.



of Waterfall Model

·        Chain reaction of delays: Due to the sequential nature of the Waterfall model, a delay in one phase can cause a ripple effect of delays throughout the project. This is because each phase must be completed before the next phase can begin.

·        Upfront cost estimation and strict adherence to the plan: The Waterfall model requires teams to estimate the cost and timeline of the project upfront. This can be difficult to do accurately, especially for complex projects. Additionally, the Waterfall model's emphasis on strict adherence to the plan can make it difficult to accommodate changes in requirements or unforeseen circumstances.

·        May take longer than other, more flexible models: This model's sequential nature can make it slower than other, more flexible models, such as Agile. This is because the Waterfall model requires teams to wait until the end of each phase to receive feedback and make changes.

·        Not flexible: The Waterfall model is not very flexible. Once a phase of the project begins, it is difficult to make changes to the plan. This can be a problem for projects where the requirements are not well-defined or where the environment is unstable.

·        Not ideal for complex and high-risk projects: This model is not well-suited for complex and high-risk projects. This is because the Waterfall model's emphasis on upfront planning and strict adherence to the plan can make it difficult to adapt to changes in requirements or unforeseen circumstances.

·        Does not handle changes well: The Waterfall model does not handle changes well. This is because the Waterfall model's sequential nature requires teams to wait until the end of each phase to make changes. This can lead to scope creep and delays.

·        No working product until the later stages of the project: This model does not produce a working product until the later stages of the project. This can make it difficult to get feedback from customers and stakeholders early on. Additionally, it can make it difficult to detect and correct errors early on.

 When to use Waterfall Model

As with all other SDLC methodologies, The Waterfall model produces the best results when 

applied in suitable environments or circumstances. Usage of the Waterfall model is less and 

less these days, as other models have built on its advantages to counter its disadvantages. 

However, the methodology remains relevant and useful if applied in the right environment. 

Some factors that determine if you need this SDLC framework for

your projects are: 

·        A project with precise requirements

·        A short project which can be easily restarted from scratch  

·        A project that involves stable and well-understood technology 

·        The risk factor is minimum 

·        Resources are readily available 

·        A project that is unlikely to require too many changes 

·        A product that does not demand extensive customer feedback 


Alternatives to Waterfall                                      

With the usage of the Waterfall model dwindling in modern times, other methodologies are 

taking centre stage. Prominent among them are:

Agile Methodology 

Agile is the software development approach that is defined by breaking down projects into small, flexible and incremental units, as opposed to a single massive launch. It aims to provide value through receipt and integration of exhaustive customer input, made easy by its flexibility, adaptability and continuously iterative nature. Agile development cycles are 

ever-evolving and constantly improving.


Spiral Model 

The Spiral model is a risk-driven framework that emphasises risk analysis and management. It combines the iterative features of other models with the structured linear 

approach of the waterfall model, only applying resources to areas with the lowest possibility of failure. The visual representation of the Spiral model is a literal spiral, with each loop representing a phase of the SDLC.


DevOps is a combination of development and IT operations teams to increase efficiency, cross-team communication, productivity and high-speed delivery in the SDLC. Its main goal is to provide high-quality software in a shortened systems development life cycle through 

collaboration between developers, operators and quality assurance personnel. 

Software and Tools for Waterfall Model

Gantt Chart 

A Gantt chart is a detailed horizontal bar chart that shows information about project management activities, resources, planning, and dependencies, as well as their timelines and deadlines.  


These charts depict sequential phases of an SDLC, enabling easy projection of dependencies and subtasks to each phase of the process. They provide a clear view of activities for each phase and their start and finish dates. It is an ideal and essential tool for the Waterfall SDLC methodology.  


Most Waterfall model software tools offer a platform for Gantt. Some of them are:



Wrike is a customisable tool that helps teams configure workflows, dashboards, and other features according to requirements. It supports an interactive Gantt chart and allows users to create and share timeline views, task dependencies, snapshots, baseline, and critical path analysis. is an online project management platform that helps teams to centralise information. It has an interactive Gantt chart that makes the Waterfall model easy to track and execute. It easily keeps track of milestones and important dates. It also features automation, real-time updates, project dashboards, and templates.


Smartsheet is a cloud-based project management platform with flexibility for use cases and 

departments. It offers a rich set of views, workflows, reports, and dashboards to capture and track your plans, resources, and schedules.


MindManager is a mapping tool that minimises the number of tools you need by offering the capabilities you need within one resource. It supports setting up the Gantt chart and easily storing, sharing, and retrieving files within the chart, adding the relevant customer requirements to the tasks and steps that need them.

Merlin Project

With Merlin Project, you can create the flow of your tasks, determine duration and dependencies, and define fixed milestones. This tool automatically transfers your input to the work breakdown view. It also helps you transform a complex plan into an elegant and expressive mind map.


The waterfall model, though less popular, remains relevant in software development and project management today due to its structured and welll organised framework. When applied to the right projects, the Waterfall model still delivers satisfactory results. 

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