Which of the following methods is NOT typically used for measuring turbidity in water?

Measuring turbidity is primarily focused on assessing the clarity of water, which is influenced by suspended particles. The methods commonly used for measuring turbidity include the Secchi disk measurement, which relies on the depth at which a disk disappears in water, and the use of a turbidimeter, an instrument that quantifies the amount of light scattered by particles in a water sample.

Visual estimation with reagents can involve using specific chemicals that change color based on the concentration of certain impurities, but it's less common than the aforementioned methods. In contrast, water sampling at various depths does not directly measure turbidity itself; instead, it is generally a procedure used to collect samples to assess other parameters such as temperature, dissolved oxygen, or nutrient concentrations at different stratified layers in a body of water. Since this method does not specifically assess turbidity, it is not typically classified as a turbidity measurement technique.