What are the standard units used to measure turbidity in water?

Turbidity in water is commonly measured in Nephelometric Turbidity Units (NTU), which is a standardized unit specifically designed to quantify how clear or cloudy water is. NTU is a measure of the intensity of light scattered at 90 degrees from a beam of light that passes through a water sample. This method is particularly useful because it considers the size, shape, and material of the suspended particles, making it a reliable indicator of water quality.

The other options represent measurement units that are suited for different parameters. For example, milligrams per liter is typically used for measuring concentrations of dissolved substances, such as nutrients or contaminants, rather than turbidity. Micrometers are a unit of length helpful in gauging the size of particles but are not applicable for measuring the cloudiness or clarity of water itself. Parts per million (PPM) is another concentration measurement often utilized for dissolved materials, but it does not directly reflect the scattering of light as turbidity does. This specificity and relevance to the measurement of suspended particles in water make NTU the appropriate choice for assessing turbidity.