A waterfall project method is a common approach adopted by projects that are focused on quality of results. Given that the waterfall project model takes a phase-by-phase approach, it becomes easy to gauge progress. However, waterfall project models have their downsides as well; here are some of them.
A waterfall project model has a sequential approach; this does not work well in all projects, and may work against the project in many cases. For instance, if there are any changes that are made in one of the previous stages then it causes disruptions in the iterative stages that follow. The co-dependency of the different phases means that you will have to make many rearrangements and modifications every time a brick in the project models is moved.
Fixed working model
A waterfall project model does not sit well with projects that have a volatile environment. If the end-project goals are not clearly defined in the conception stage, and are capable of changing during the course of the project, a waterfall model will not be able to adapt to these changes. Same goes with long-standing projects, which are likely to evolve with market changes, and need a dynamic project model.
Rectifications and modifications
It becomes difficult to trace back and make modifications in a waterfall project model. Take a software project for instance; once it is in the testing phase, going back to the development cycle and making changes in the source code, due to inadequate planning at the initial stage makes things difficult.
In a waterfall or linear sequential model, the input from one phase is taken for the next phase, as the project progresses. The problem with this is, often, the results are not visible until the end of the project life cycle. This makes it difficult to evaluate whether or not the project is being spearheaded in the right direction unless a similar project has previously shown success with the same project template.
Clarity on deliverables
A waterfall project model is developed around the deliverables of the project. In some projects, you may not have clarity on the deliverables in the initial phase, in which case the waterfall project model cannot be adopted. Without a clear-cut definition of the product and technology, this approach falls through. This again, makes the waterfall project model a not so versatile solution in a project management scenario.