Prepared by Deana Crumbling
Turbidity is the measure of the cloudiness of water. It is
Remember: It is more accurate to perform the test immediately
at stream-side. To do so, you must take along a small bottle
of tap water.
- Fill one of the cylinders to the 50 mL mark with stream water
and the other with tap water. If the water appears very turbid/cloudy,
fill the cylinders only to the 25 mL mark.
- SHAKE the bottle of Standard Turbidity Reagent vigorously
to resuspend the latex particles in the reagent.
- To the cylinder containing TAP WATER, use the dropper to
add Standard Turbidity Reagent in 0.5 mL increments-(NOT drop-by-drop).
Add 1 squirt of 0.5 mL Reagent, then use the plastic stirring
rod to mix.
- Compare the fuzzy appearance of the black dot at the bottom
of the tap water cylinder with the dot in the stream water cylinder
(DO NOT try to match the color-the latex particles are white
and will never match the brownish or greenish tint of most stream
water). The goal is to add enough of the Standard to the tap
water so that the cloudiness (as judged by the appearance of
the black dots) of the tap water is made to match that of the
- Count the number of "squirts" required to get a
match. Read the turbidity (in units called JTU) off the chart
on the kit's package insert/directions. Make sure you read off
the correct column-one column is for use with a 50-mL volume,
the other column is for a 25-mL volume.
- On the reporting sheet, fill in the result and the number
of squirts and test volume used. Examples: 15 JTU (3 squirts/50
mL) or 30 JTU (3 squirts/25 mL)
- If the stream water looks just as clear as the tap water,
report the result as "less than 2.5 JTU" by circling
that option on the SOS Report Sheet.
- If the stream water looks a little more cloudy than the tap
water at the start, but when you add 1 squirt of turbidity reagent
it looks like the tap water column becomes much cloudier than
the stream water, report the result as "about 2.5 JTU"
by circling that option on the Sheet.
Tip: If you are not sure if you have a match, add another
squirt of turbidity reagent. If you can see that you've "gone
ever," you can feel sure that the previous number of squirts
was indeed the correct number.
Note: You may interpolate your result, if you wish.
For example, if the match seems like it was between squirts
2 and 3 for a 50 mL volume, you could report the result
as " ~12.5 JTU" (which means "about half-way
between 10 and 15 JTU"). Or you could use the higher
number (15 JTU) or the lower number (10 JTU), whichever
one you feel is closest to the match. Any of these choices
is acceptable, since the turbidity measurement is only an
Turbidity Test Results
|Number of Measured Additions
||Amount in mL
||50 mL Graduation
||25 mL Graduation