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| Turbidity is the amount of solid particles suspended in water that causes light rays shining through the water to scatter. Too much turbidity will make water cloudy or in the extreme case, muddy. Turbidity is measured accurately with a nephelometer (turbidimeter) in units called nephelometric turbidity units, or NTUs. Most states limit drinking water to a maximum of .5 NTUs, however usually drinking water is .1 NTUs or less. High levels of turbidity can affect aquatic life in several ways. Too much turbidity might make it difficult for plants to complete photosynthesis, which in turn affects the amount of dissolved oxygen. If the levels get too low the algae and plants may die which then decays which uses more oxygen making the problem even worse. Too much silt can also clog the gills of fish and other organisms. Large suspended particles may create a place for harmful bacteria to live. Fish cannot see well in turbid water making finding food difficult. |
METHOD 1
Visually observe stream or river
Visually observe whether the water is clear, cloudy, or muddy, according to the chart below:
Clear |
Objects on bottom of stream can be seen clearly |
Cloudy |
Objects on bottom of stream can be detected but not identified |
Muddy |
Objects on bottom cannot be seen |
METHOD 2
Using transparency tubes
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| 1. Fill one transparency tube with tap water from home school (for clear water reference). | 2. Fill the other transparency tube with water sample to be tested. | 3. Looking straight down into the tubes, visually observe ability to see black and white disk on the bottom of the tube (see chart below): |
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| Sample from stream. | Sample from home school (tap water). |
Clear |
black & white disk can be seen clearly |
Cloudy |
black & white disk can be seen, but not clearly |
Muddy |
black & white disk cannot be seen |
METHOD 3
Using a nephelometer (turbidimeter)
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1. Put water sample to be tested in nephelometer bottle. |
2. Wipe outside of bottle with soft, clean cloth - be sure to remove all fingerprints, etc. | 3. Gently place bottle into the nephelometer (turbidimeter). |
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4. Push the "Read" button. |
5. Record results in NTUs (nephelometric turbidity units). |
| Turbidity |
Approximate reading in NTUs |
Clear |
0-3 NTUs |
Cloudy |
4-12 NTUs |
Muddy |
>12 NTUs |
