Waterfall

Waterfall is the traditional, sequential approach to projects — requirements, design, build, test and deploy done as distinct phases, each completed before the next begins.

Waterfall is a predictive, plan-driven project methodology in which work flows downward through a fixed sequence of phases — typically requirements, design, implementation, verification and maintenance — with each phase completed and signed off before the next starts. It assumes requirements can be defined up front and will remain stable, and it front-loads planning so that scope, schedule and cost are baselined early. It contrasts with Agile, which delivers iteratively and expects requirements to evolve.

Why it matters

Waterfall’s clarity is its value: when requirements are genuinely known and stable, a sequential plan with defined phase gates gives strong predictability, clear documentation, and easy progress tracking against a fixed baseline. It is well understood, contracts and budgets map cleanly onto its phases, and regulated or physical projects often require its rigour and traceability.

When to use it

Use Waterfall when requirements are well understood and unlikely to change, the technology is proven, and predictability matters more than flexibility — construction, manufacturing, infrastructure, and compliance-driven work. Avoid it when requirements are uncertain or evolving, where its high cost of late change becomes a liability.

How to use it

1. Gather and document all requirements up front and get them signed off.
2. Produce a complete design based on those requirements.
3. Build the solution according to the design.
4. Test and verify against the original requirements.
5. Deploy, then maintain — with changes handled through formal change control.

Example

A bridge construction project uses Waterfall: the design is fully engineered and approved before any concrete is poured, because changing the foundations after building is enormously expensive. Each phase — survey, design, foundations, structure, finishing — completes and is inspected before the next begins.

Template

A Waterfall project relies on a requirements document, a full project plan/Gantt, phase-gate checklists and a change control process.

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Alternatives

• Agile — iterative and adaptive
• V-Model — Waterfall variant emphasising testing at each stage
• Hybrid — Waterfall phases with Agile execution inside them