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Chapter 3

Chapter 3 Textbook Notes

Environmental Science
Course Code
Jovan Stefanovic

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Human Health and Environment: Chapter 3 Water Quality and Water
Resources (Textbook reading)
Safe drinking water is a need ; we depend on plentiful and drinkable (clean) water
but we are facing issues with water quality and quantity
Water supply faces old threats and new threats
oOld threats: human and industrial wastes
oNew threats: demand overload and climate change
There are lots of waterborne infections that have existed since the 19th century
oDiarrhoeal deaths due to waterborne infections kill over 2 million children
oDiarrhoeal illnesses are the result of drinking contaminated water
Widespread use of oral rehydration therapy has reduced waterborne disease related
deaths. However, there is very little being done to improve water and sanitary
infrastructure in developing countries
Updating the means of disposal of human wastes improves human health to a
greater extent than providing clean water supplies
Sources of Drinking Water
Usually comes from surface water (e.g. streams, rivers, and lakes) or ground water
through artesian or other types of wells
Other sources collecting rain water or desalinating sea water (taking the salt out
of salty, seawater)
Surface water more prone to contamination by both microbial pathogens and
chemicals since it directly receives industrial and municipal wastewater and runoff
from the land
oPathogen: any disease-producing agent, especially a virus, bacterium, or
other microorganism.
Ground water usually less contaminated than surface water b/c the soil which it
filters/seeps through serves as a filter
EXCEPTION: groundwater can get contaminated if

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oEx 1: there is a direct or short path from surface to groundwater, when
concentrated wastes deep in the soil leach into groundwater, as beneath a
oEx 2: when wastes are injected directly into the ground
Once chemicals enter groundwater, it is contaminated for a long period of time b/c
groundwater collects slowly and doesnt quickly replenish itself
Uses of Water
Human consumption of water (e.g. drinking and using water to cook) is one of the
smallest uses of water
70% of water is used to irrigate agricultural land (88% of irrigational water is used
by Africa, 31% in Europe)
Industrial uses of water are substantial usually used to cool or flush equipment.
The water is then usually returned to streams, rivers or coastal waters (the returned
water often ends up being warm or contaminated by chemicals
Tap water at home mostly used for flushing toilets, washing clothes, showering ,
watering lawns and cars
Sources of Contamination
Many chemical s (e.g. pesticides and fertilizers) enter drinking water sources after
being deliberately applied to land or even ponds & streams and washing into surface
or ground water
Animal wastes enter drinking water in a similar fashion as above
Industrial waste chemicals and municipal wastes containing human fecal material
and whatever chemicals have entered the system may be directly discharged into
surface water (esp. in developing countries)
Other chemicals reach drinking water sources after moving through soils
a.E.g. cadmium and other heavy metals can leach out of dumps and landfills
while gasoline products and additives can contaminate drinking water
through leakage from storage tanks
b.Toxicants like arsenic and radon occur naturally in the earths crust and
contaminate groundwater that is in contact w/ deposits of these substances

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c.Our methods of treating and distributing drinking water lead to some
chemicals (e.g. disinfection by products and lead) being present w/i our
drinking water supplies)
Point Sources: sources of contaminants that discharge into receiving water from a
pipe, industrial waste plant, sewage treatment plant or any other identifiable device
a.Developing countries are susceptible to point source contamination due to
lack of enforced laws. Developed countries are less susceptible due to laws
such as the Safe Drinking Water Act
Non-point sources: sources of contaminants that cannot be defined by discrete pipes
or other devices (e.g. agricultural runoff, the runoff of oils and other chemicals from
streets and highways, multitude of leaking septic systems and gasoline storage tanks
and airborne emissions of mercury and other substances that may settle on and
dissolve in drinking water)
a.Drinking water is vulnerable to contamination from non-point sources
Water Treatment Process
To reduce the burden of waterborne diseases outbreaks, developed countries implement a
process to treat drinking water (takes out tiny particles like microbes out of water. Doesnt
take out chemicals to a significant degree):
1.Water is pumped from its source
Surface waters containing sediment and microbial pathogens may be held in
settling tanks or pre-treated w/ chlorine at this stage
2.Add chemical coagulant (usually containing alum) to make small particles (e.g. small
pieces of decaying organic matter or microbes) to stick together in the water
Coagulant: a substance that produces or aids the change of a fluid into a
thickened mass
3.With flocculation, the collecting particles are stirred to make them adhere & become
larger and heavier
Makes particles more likely to sink to the bottom of holding tanks in the next
step sedimentation
*** Water with chemical contamination may need to undergo additional
treatment at this stage. E.g. activated charcoal or special ion exchange resins ****
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