NTU 1
NTU 1 :
Abbreviation for nephelometric turbidity unit, a unit used in measuring water quality. Turbidity is an optical property: the scattering and absorption of light by solids suspended in water. Turbid water has a cloudy or hazy appearance. An instrument called a nephelometer (from a Greek word meaning "cloudy") measures turbidity directly by comparing the amount of light transmitted straight through a water sample with the amount scattered at an angle of 900 to one side; the ratio determines the turbidity in NTU's. The instrument is calibrated using samples of a standard solution such as formazin, a synthetic polymer. Drinking water should not have a turbidity above 1 NTU, although values up to 5 NTU are usually considered safe. Outside the U.S., this unit is usually called the FNU (formazin nephelometric unit)
