Nephelometric Turbidity Units (NTU) are most commonly used to:

Nephelometric Turbidity Units (NTU) are a standard measurement used to quantify the turbidity or cloudiness of water. Turbidity is an important parameter in water quality assessment as it indicates the presence of suspended solids, which can be organic or inorganic materials. These particles can scatter light, making water appear murky or unclear. The NTU measurement specifically indicates how much light is scattered by these particles in a water sample when illuminated by a light beam, which is crucial for understanding the clarity of water.

Measuring turbidity is significant for both drinking water quality and environmental assessments since high turbidity levels can affect aquatic life, water treatment processes, and the aesthetic quality of water. Therefore, using NTU to determine turbidity directly aligns with their purpose and makes this the correct answer. The other options suggest measurements related to pollution types, dissolved oxygen, or wastewater strength, none of which directly relate to the specific function of NTU in quantifying turbidity.