Turbidity (NTU and JTU)

What is turbidity?

Water turbidity measures how cloudy a sample of water is as a result of suspended particles. Since these particles occur as a result of both sediment erosion and plankton growth, turbidity can indicate the general state of stream processes for a location.

Why is it important?

Turbidity in open water may be caused by growth of phytoplankton or human activities such as construction, mining and agriculture which enter the bodies of water water due to rain storm runoff. In lakes and rivers, high levels can mean very little light is reaching the bottom, which can prevent growth of submerged plant life and as such affect aquatic species which are dependent on them for nutrients. High levels can also affect the ability of fish gills to absorb dissolved oxygen.

How do I measure it?

Turbidity is commonly measured using a nephelometer which uses a light beam (source beam) and a light detector (usually at a 90° angle) set to one side of the source beam. The units from a calibrated nephelometer are called Nephelometric Turbidity Units (NTU).

  • 1 NTU: Common measurement for tap water.
  • 1 NTU: Common regulatory limit for drinking water quality.

An alternative unit is JTU. The Jackson Turbidity Unit (JTU) is a historical measurement done with the Jackson Candle Turbidimeter. To use this measurement tool, the tester pours water into a tube positioned over an open flame until the flame is no longer visible! This is not a common method these days — modern meters can measure this value with no flames involved. Read more about Jackson Candle Turbidimeters.

Water Rangers Protocol

While we do not currently have a test for this in our kit, you can certainly look at water clarity as an indicator. Typically a turbidimeter or turbidity sensor is used for this test.