Waterfall — Explained with Examples

Waterfall is a sequential (linear) software development model where progress flows in one direction through distinct phases: Requirements → Design → Implementation → Verification → Maintenance. Each phase must be fully completed before the next begins, and there is typically no going back.

Originating from manufacturing and construction (where rework is extremely expensive), Waterfall was formalized by Winston W. Royce in 1970 — ironically, Royce himself criticized the model and advocated for iteration. Waterfall works well when requirements are stable, well-understood, and unlikely to change. However, it is rigid: if a requirement error is discovered during testing, the entire project may be delayed while waiting for the requirements phase to be revisited.

Real-world analogy. Waterfall is like building a house. You cannot start framing walls (Design) before the foundation (Requirements) is poured. You cannot wire electricity (Implementation) until the walls are built. Changing the floor plan after construction begins is extremely costly.

Example (Phases):

Phase 1: Requirements  ──→  "Customer needs login system"
Phase 2: Design        ──→  "Database schema, API design"
Phase 3: Implementation ──→  "Write code"
Phase 4: Verification  ──→  "Test login flow"
Phase 5: Maintenance   ──→  "Fix bugs post-release"

Related terms: Agile, Scrum, Spike, MVP, Technical Debt

Related tutorial: Waterfall vs Agile