What does a venturi tube mainly measure in water flow?

A venturi tube is designed to measure the rate of water flow through it by utilizing the principle of continuity and Bernoulli's equation. When water flows through a venturi tube, it passes through a section that narrows, causing the velocity of the water to increase and the pressure to decrease. By measuring the pressure difference between the wider and narrower sections of the tube, the flow rate can be calculated. This makes venturi tubes highly effective and commonly used devices in various applications for determining flow rates in water systems.

The other options focus on different aspects of water quality or composition, which are not related to the primary function of a venturi tube. For example, measuring chlorine levels or suspended solids requires specific analytical techniques that assess the chemical and particulate content of the water rather than its flow characteristics. Similarly, water clarity is typically determined through turbidity measurements or other direct visual assessments, which do not involve flow rate measurements. Therefore, option C accurately captures the fundamental role of venturi tubes in assessing the dynamics of water flow.