Basic Water Quality - Pleasanton Unified School District

What is Turbidity?
 A measure of water clarity
 The murkier the water, the higher the
 Turbidity reduces the transmission of
light into water.
 Turbidity increases as a result of
suspended solids in the water.
Sources of Turbidity
Phytoplankton blooms
Soil erosion
Waste discharge
Urban runoff
Abundant bottom feeders
Why is Turbidity Important?
• Suspended particles diffuse sunlight and
absorb heat.
• As temperature increases, DO decreases.
• Suspended solids can clog fish gills
• Less light is available for photosynthesis.
• As sediment settles, gravel beds become
How is Turbidity Measured?
Secchi disk
– Measures water
– Measures depth
at which disk is
no longer visible
– Useful for deep
Turbidity in the lab and field
– optical device that
measures scattering
of light (most
– Measure in NTU
turbidity units) or
JTU (Jackson
turbidity units)
What is the Turbidity of our
 5 NTU’s = maximum contamination
level allowed (MCL)
 0.45 NTU = highest average turbidity
from a local well
 0.15 NTU = highest level found at Del
Valle Water Treatment Plant
Typical Turbidity Data
Water Source
Turbidity Level
Water bodies with sparse plant and
animal life
Drinking water
<0.5 JTU
Typical groundwater
<1.0 JTU
Water bodies with moderate plant and
animal life
1 - 8 JTU
Water bodies with large plumes of
planktonic life
10 - 30 JTU
Muddy water or winter storm flows in
20 - 50 JTU
Water Quality Testing and Monitoring Program for Middle Schools and High Schools. San Diego County Water Authority.
So what?
– Increase in turbidity in reservoirs in
southwestern U.S.
– Increase in turbidity in Delta waters during
dry years
Degrades drinking water quality.
Water treatment costs increase.
Decreases light penetration in water.
Can clog gills of fish.
What is Conductivity?
• Conductivity is the measure of water’s
ability to conduct an electric current.
• Estimates amount of total dissolved
minerals (ions).
Conductivity in water
• Dissolved salts
(ions) conduct
electrical current in
• Absolutely pure
water is a poor
electrical conductor.
How do we measure
• Test with a
Conductivity meter
• Measured in
Siemens or
Conductivity Units
• Mhos is ohms backwards! (Mhos is the
reciprocal of ohms –if you have to know)
• So….ohms is a measure of the resistance to
a current.
• The less the resistance, the greater the
• Conductivity in drinking water is low, so we
use µmhos/cm or 1 x 10-6 mhos/cm!
• Units are sometimes expressed as
microsiemens (µS).
Conductivity and Turbidity
• Use of lightbulb as class demo
• Use of conductivity meter
• Use of probeware
• Kit Secchi disk
Some Conductivity Data
Water Type
Distilled Water
0.5 - 3.0
Melted snow
2 - 42
Potable water in U.S.
30 - 1500
Irrigation Supply Water
< 750
Water Source
Sea water
33 - 37
Salton Sea
Mono Lake
So What?
• Increased concentration of salts increases
the conductivity
• Salts cannot be filtered out
• Higher conductivity can.…
– Foul irrigation water (leads to high salinity soils)
– Kill wildlife
– Create water shortages
Salt water and cells
•Salt water is hypertonic to the cells of some plants
•This causes plants to wilt and possibly die

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