03 Water Purification: Contaminants:
Description
This article is from the Water Treatment FAQ, by Patton Turner with numerous contributions by others.
03 Water Purification: Contaminants:
Heavy Metals:
Heavy metals are only a problem is certain areas of the country. The
best way to identify their presence is by a lab test of the water or
by speaking with your county health department. Unless you are down
stream of mining trailings or a factory, the problem
will probably affect the whole county or region. Heavy metals are
unlikely to be present in sufficient levels to cause problems with
short term use.
Turbidity
Turbidity refers to suspended solids, i.e. muddy water is very turbid.
Turbidity is undesirable for 3 reasons 1)aesthetic considerations 2)
Solids may contain heavy metals pathogens or other contaminants, 3)
turbidity degreases the effectiveness of water
treatment techniques by shielding pathogens form chemical or thermal
damage, or in the case of UV treatment, absorbing the UV light itself.
Organic compounds
Water can be contaminated by a number or organic compound such as
chloroform, gasoline, pesticides, and herbicides. These contaminants
must be identified in a lab test. It is unlikely ground water will
suddenly become contaminated unless a quantity of
chemicals is allowed to enter a well or penetrating the acquifer. One
exception is when the aquifer is located in limestone. Not only will
water flow faster through limestone, but the rock is prone to forming
vertical channels or sinkholes that will rapidly allow contamination
from surface water. Surface water may show great swings in chemical
levels due to differences in rainfall, seasonal crop cultivation, and
industrial effluent levels
Pathogens:
Protozoa: Protozoa cysts are the largest pathogens in drinking water,
and are responsible for many of the waterborne disease cases in the
US. Protozoa cysts range is size from 2 to 15 um (a micron is one
millionth of a meter), but can squeeze through smaller openings. In
order to insure cyst filtration, filters with a absolute pore size of
1 um or less should be used. The two most common protozoa pathogens
are Giardia Lamblia (Giardia) and Cryptosporidium (Crypto). Both
organisms have caused numerous deaths is recent years in the US, the
deaths occurring in the young and elderly, and the sick and immune
compromised. Many deaths were a result of more than one of these
conditions. Neither disease is likely to be fatal to a healthy adult,
even if untreated. For example in Milwaukee in April of 1993, of
400,000 who were diagnosed with crypto, only 54 deaths were linked to
the outbreak, 84% of whom were AIDS patients. Outside of the US and
other developed countries, protozoa are responsible for many cases of
Amebic dysentery, but so far this has not been a problem in the US,
due to better wastewater treatment. This could change during a
survival situation. Tests have found Giardia and/or crypto in up to
5% of vertical wells and 26% of springs in the US.
Bacteria:
Bacteria are smaller than Protozoa and are
responsible for many diseases such as typhoid fever, cholera,
diarrhea, and dysentery. Pathogenic bacteria range in size from .2 to
.6 um, and a .2 um filer is necessary to prevent transmission.
Contamination of water supplies by bacteria is blamed for the cholera
epidemics which devastate undeveloped countries from time to time.
Even in the US, E.coli is frequently found to contaminate water
supplies. Fortunately E. coli is relatively harmless as
pathogens go, and the problem isn't so much with E. coli found, but
the fear that other bacteria may have contaminated the water as well.
Never the less, dehydration from diarrhea caused by E. coli has
resulted in fatalities.
Viruses:
Viruses are the 2nd most problematic pathogen, behind protozoa. As
with protozoa, most waterborne viral diseases don't present a lethal
hazard to a healthy adult. Waterborne pathogenic viruses range in
size from 0.020-0.030 um, and are too small to be filtered out
completly by a mechanical filter (better filter designs, such as the
Katadyn may remove as much as 99% of viruses.) All waterborne enteric
viruses affecting humans occur solely in humans, thus animal waste
doesn't present much of a viral threat. At the present viruses don't
present a major hazard to people drinking surface water in the US, but
this could change in a survival situation as the level of human
sanitation is reduced. Viruses do tend to show up even in remote
areas, so acase can be made for eliminating them now.
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