Basic Property – Compressibility of Water Statement: For most engineering calculations at ordinary pressures, water is treated as an incompressible liquid.

Introduction:
This question targets the standard modeling assumption regarding water compressibility in fluid mechanics and hydraulics. Recognizing when water can be idealized as incompressible simplifies analysis significantly.

Given Data / Assumptions:

• Ambient temperatures and moderate pressures typical of water supply systems.
• Small density changes under pressure relative to gases.

Concept / Approach:

Compressibility describes density change with pressure. Water has a high bulk modulus, so density varies very little with pressure in common applications. Thus, continuity and momentum equations often assume constant density (incompressible flow).

Step-by-Step Solution:

Verification / Alternative check:

Compare typical density variation of water under several MPa to that of air; water changes are orders of magnitude smaller, supporting the incompressible idealization.

Why Other Options Are Wrong:

A compressible: Overly general for routine conditions. Weakly compressible only at very high pressure: Although qualitatively true, the statement in the stem asks for the standard classification used in typical calculations. Ideal gas: Physically incorrect.

Common Pitfalls:

Assuming perfect incompressibility even for rapid transients (e.g., water hammer) where compressibility matters; confusing thermodynamic compressibility with modeling simplifications.

Final Answer:

an incompressible