Which three devices are most commonly used for measuring flowing water?

Prepare for the American Water Works Water Treatment Plant Operator Test. Study with multiple choice questions, each with hints and explanations. Get ready to excel!

Measuring flowing water effectively relies on devices that translate either open-channel depth or pressure differences into a discharge reading. A weir is for open channels and uses the water height over a sharp crest to determine flow with a standard relationship; it’s simple, robust, and inexpensive, so you’ll see it commonly in channels carrying plant inflow or wastewater. A Parshall flume also serves open-channel measurement, but its standardized shape constrains the flow so a specific depth at the throat maps to a known discharge, giving reliable readings over a wide range and reducing sensitivity to upstream conditions. For pipes and other closed conduits, a Venturi meter is favored because it creates a measurable pressure drop across a constricted throat; applying the Venturi principle lets you calculate flow with good accuracy and relatively low head loss.

Other options exist but aren’t as widely used as primary flow meters in typical water treatment operations. An orifice plate provides differential pressure but can be more sensitive to upstream conditions and may introduce more head loss at variable flows. A Pitot tube measures velocity at a single point and doesn’t directly yield overall discharge without extensive traversing and calculations. A float valve is a level-control device, not a flow meter.