Problems with the Waterfall Model

1. Real projects rarely follow the sequential flow that the model proposes. Although the Waterfall model can accommodate iteration, it does so indirectly.
2. It is often very difficult for the customer to state all requirements explicitly. The Waterfall model has the difficulty of accommodating the natural uncertainty that exists at the beginning of many projects.
3. The customers must have patience. A working version of the program(s) will not be available until late in the project time-span. A major blunder, if undetected until the working program is reviewed, can be disastrous.
4. The difficulty of accommodating change after the process is underway.
5. One phase has to be complete before moving onto the next phase.
6. Few business systems have stable requirements.