Water Treatment Guidelines for Emergency Response
By: Cory Lancaster
There will be two categories of needs for water purification to prevent loss of life
due to waterborne diseases during relief efforts. The first category consists of short term
systems that need to be delivered immediately to affected areas as soon after a disaster
occurs to provide survivors with safe drinking water. This assumes the existing water
supply has been or will soon be seriously contaminated and the existing water/wastewater
conveyance infrastructure has been impaired. These systems need to be self contained
and easily transported. As disaster areas are often without power and transportation to
and from these areas may be difficult, a compact generator and fuel or a solar system
needs to be supplied. Ideally, there may be systems that meet these requirements that are
powered mechanically, such as by a foot or hand powered pump. The second category is
comprised of long term water purification systems that are installed during rebuilding
efforts, and is not addressed here.
Most importantly during emergencies is the removal of bacteria (responsible for
typhoid and gastroenteritis (Salmonella), bacillary dysentery (Shigella), cholera (Vibrio
cholerae), and diarrhea (many genus)), protozoans (responsible for amoebic dysentery
(Entamoeba histolytica) and diarrhea (including Giardia lamblia and Cryptosporidium
parvum), and helminthes (parasites including Hookworm, Roundworm, Tapeworm,
Threadworm and Tapeworm) and viruses. Viruses are extremely small, ranging in size
from 20 to 100 nm. Most bacteria typically range in size from 0.5 to 2μm , protozoan
cysts range from 5 to 15 μm, and helminthes from 40 to 60 μm. If all contaminated water
was merely filtered to 0.45 um and these organisms were effectively removed from the
potable water supply, nearly all those diseases listed except those caused by viruses could
be prevented. Due to their small size, viruses cannot practically be removed through
filtration, and need to be removed through disinfection, which, for emergency situations,
would most practically be ultraviolet light exposure. Chlorine or iodine will inactivate
viruses with an appropriate residual and contact time after adequate filtration, and may be
an alternative disinfection option by adding small quantities to contaminated drinking
water, which can then be consumed without harm. It is important to note that in order for
most organisms to be destroyed, particulates must be removed to the greatest extent
possible, as pathogens may be occluded in particles, rendering the disinfection method
ineffective. Additionally, it is important to be aware that some microorganisms, such as
the larger sized protozoa, are extremely resistant to chlorination and must be removed by
filtration, although they are readily inactivated with UV light. A majority of the concern
regarding drinking water quality during relief efforts surrounds preventing these diseases.
However, there are other contaminants that should be removed if possible.
Certain soluble and volatile organics are carcinogenic, and pesticides and herbicides can
be toxic. Most of these compounds may be removed though activated carbon filtration.
This is an important step if disinfection through chlorination were to follow, as soluble
organics will react with chlorine to form disinfection byproducts, eg., trihalomethanes,
which are often carcinogenic. Keep in mind that reducing carcinogen exposure is
probably a much lower priority than preventing contraction of a waterborne disease,
which may be deadly in the short term. Inorganic chemicals may also be present, such as
heavy metals and nitrate. Heavy metals such as lead and mercury are bio-accumulative
and have significant neurological effects, while excess nitrate in drinking water as a result
of contamination with wastewater and agricultural runoff and may result in
methemoglobinia in infants (of concern when concentrations exceed 10mg/L), while high
concentrations have little or no affect on adults. While most heavy metals may be
removed through activated carbon filtration, biological or chemical reduction is needed
for denitrification of nitrate to nitrogen gas. In general, though, these contaminants are of
much less concern during emergency situations, as acute exposure is not immediately life
threatening (unless in high concentrations) and assuming that emergency water supply is
temporary. Also, if the water supply is brackish (contaminated by salt water), water
needs to be passed through a Reverse Osmosis (RO) filter, which requires adequately
filtered water to begin with, or distilled, which are both energetically intensive. Avoid
having to treat brackish water if at all possible.
Generally, in an emergency situation, any moderate attempts to treat contaminated
drinking water will save lives. Multi-stage filtration alone (down to 0.45 μm) will
dramatically improve water quality. If gravity fed filtration system is utilized, no power
is needed whatsoever – buckets of water are emptied into the top of the system, and no
electricity is needed to power a pump or UV light, but there is no destruction of viruses or
any other microorganism that may pass through the filter, however unlikely. This water
may be ideal for washing or uses other than consumption if viral contamination is a
concern. They have the added benefit of being much more affordable to complete
treatment systems, but treat water at a much slower rate. Higher levels of treatment are
more costly but will result in lower incidence of preventable deaths, such as those
resulting from viral infections. That being said, nearly all waterborne pathogens may be
removed from contaminated drinking water with the proper use of a portable, self
contained water purification system complete with disinfection.
In summary, there are some features that are required for a highly effective
emergency response water purification system. Multiple levels of physical filtration are
needed, to remove particulate matter and pathogenic organisms such as bacteria,
protozoans, and helminthes. These filters must be maintained, either through periodic
cleaning or replacement. Ceramic filters are the most expensive, but generally better than
others as they can be cleaned. An activated carbon filter should follow to remove
organics, metals, pesticides and herbicides. A gram of activated carbon has an equivalent
surface area of a football field and has a very high adsorption capacity. Following an
activated carbon filter should be a disinfection system, if it is so desired or can be
afforded. In order to remain portable and self contained, a UV light source is ideal. It is
imperative to keep in mind that if the disinfection step is to be as effective as the
manufacturer claims, all of the preceding filters must be functioning properly.
Additionally, the UV light itself must be in working order, which may be difficult to
determine, as most UV light casings are enclosed and UV light itself is undetectable to
the naked eye. The pumping system and the UV system must have power, through either
a gas generator, solar power, or some other method (human-powered). Finally, the
system must be used in a way that prevents contamination of the delivery end of the
treatment system. While no system is 100% effective, claims made by the manufacturer
should be trustworthy if all of these measures are followed.