Fourteen years ago, I traveled to St. Petersburg, Russia, to study
abroad. There I found what I had expected: magnificent art and
architecture, the canals and rivers that make St. Petersburg the “Venice
of the North,” ballet and opera in the Mariinsky Theater, and some of
the most highly educated, culturally aware people I have ever met
anywhere. But I also found something I had not expected: I couldn’t
drink water straight from the tap. If I did, I would apparently get
giardiasis, a parasitic infection that can cause severe diarrhea. So,
every time I drank water, I either filtered it myself, or used boiled
water, or purchased bottled water. All this extra effort made me much
more conscious of my use of water, and my need for it. I thought about
the safety of my water every time I took a drink, brushed my teeth,
bathed or washed my clothes, and I worried about how it might affect my
health. And then I started thinking about all the people in the world
who must wonder and worry about water every day. Even with years of
progress in water and sanitation, more than 780 million people still do
not have access to safe water. For these people, who comprise 11% of
the world’s population, the only drinking water available poses a threat
to their health, and possibly to their lives.
According to UN Secretary-General Ban Ki-moon, unsafe water causes
more deaths worldwide than war.(2) Diarrheal diseases, which spread
through unsafe water, kill 1.8 million people every year, 90 percent of
whom are children younger than five.
On average, a child dies every 23 seconds from unsafe water and lack of adequate sanitation.
When water-related disease does not kill, it maims. Children who
survive repeated diarrheal diseases may also suffer from malnutrition,
further weakening them and increasing their susceptibility to
infection. They miss school days and, with chronic water-related
infections such as malaria or schistosomiasis, may suffer long-term
cognitive impairment and delays. Many water-related diseases
permanently disable their victims, such as trachoma, which causes
extremely painful eye infections, predominantly in women and children,
and can ultimately lead to blindness.
Diseases related to unsafe water account for more than 60 million disability-adjusted life years lost worldwide.
Unsafe water can contain many different types of pathogens, including bacteria, viruses, and parasites.(6) Human
feces is often the source of these contaminants, due to insufficient
separation of human waste from water supplies. Adequate disposal of
human waste—basic sanitation—is therefore a critical requirement for
preventing water-related disease.
Two and a half billion people in the world do not have access to
improved sanitation, defined as the hygienic separation of human excreta
from human contact. Of these, more than one billion practice open
defecation, which means that they do not have access to any sanitation
facilities and must instead defecate in the bush or open fields.
Contamination of water sources with human excreta leads to transmission of a variety of water-related diseases. To clarify the various roles of water in disease transmission and facilitate effective public health interventions, David Bradley and colleagues published a classification system for water-related disease in 1972, using four basic categories:
Waterborne diseases occur upon ingestion of water containing a
pathogen. Disease transmission by this route results from fecal
contamination of water, and is known as fecal-oral. Most diarrheal
diseases fall into this category, including cholera, dysentery, and
typhoid fever.
Water-washed, or water-scarce, diseases occur when people do not have
enough water to fulfill their basic personal hygiene needs, such as
washing their hands with soap, and/or bathing or doing laundry often
enough to remove bacteria and mites from skin, bedding and clothing.
Water-scarce diseases include scabies, caused by mites transmitted from
skin-to-skin or (more rarely) via clothing and bedsheets, and trachoma,
caused by bacteria that are secreted in eye discharge, which then
spreads either by flies that land on the eyes, or by direct
person-to-person contact. Diseases classified as fecal-oral can also
fall into this category, because pathogens excreted in feces can be
transmitted from unwashed hands to food or water, and then ingested.
Water-based diseases occur when a human host encounters and is
infected by a pathogen that both multiplies and infects while in the
water. Schistosomiasis, a parasitic infection that completes part of
its life cycle in aquatic snails, is an example of this type of disease.
Finally, water-related insect vector diseases are spread by insects
that breed in or bite near water. This category includes malaria and
dengue fever, which are transmitted via mosquito vectors.
Interventions intended to reduce the incidence of water-related
insect vector diseases have often focused on either killing or blocking
the insect vector, developing a vaccine against the causative agent, or
modifying human behavior to reduce contact with the insect vector.
Classifying these diseases as water-related, however, suggests different
approaches to preventing their transmission, considering not just the
vector or causative agent of disease, but also its environment.
Potential interventions to reduce the spread of vector-borne,
water-related disease include:
• modifying the environment to transform stagnant water into flowing water to prevent mosquito breeding
• designing and engineering dams and other water-related construction
projects to distance standing water sites from human settlements
• introducing fish that eat mosquito larvae into bodies of stagnant water near humans
• implementing environmental assessments to identify and remove
standing water from areas near humans, including rainwater storage,
discarded tires, etc, in order to interrupt the mosquito life cycle.
Interventions to prevent transmission of waterborne,
water-washed/water-scarce and some water-based diseases focus on three
objectives: cleaning water by removing or inactivating pathogens,
improving sanitation, and increasing personal hygiene.
Removing pathogens and other contaminants from water can be either a
highly elaborate process, as with the multi-step filtration and
flocculation procedures undertaken in water treatment plants, or
extremely simple, such as point-of-use filtration through folded sari
cloth. Pathogens can also be inactivated in water by chemical treatment or UV irradiation.
Interventions to improve water quality have been shown to reduce diarrhea incidence by as much as 35 percent, if sustained.
Efforts to increase water quantity—independent of water quality, just
to give people enough water for bathing and washing—yield 6 to 25
percent reductions in diarrhea morbidity. Having more water is an improvement, even if it is unsafe to drink.
Sanitation improvements can also involve either highly elaborate
interventions, such as flush-water toilets (which require a piped
plumbing system), or comparatively simple efforts, such as a pit
latrine. A pit latrine consists
of a deep, lined pit covered by a concrete slab with a hole in the
center and sheltered by a structure containing a roof and a door.
Simple pit latrines can be constructed for as little as $26, providing an improved sanitation alternative to open defecation.
Improved sanitation reduces diarrhea morbidity by as much as 36 percent, and can reduce infant deaths by 40 to 59 percent, depending on the country studied.
Interventions to promote hygiene are also highly efficacious.
Hand-washing with soap, one of the simplest and most effective
improvements to hygiene, has been shown to reduce the incidence of
diarrheal disease by 40 percent.
Cost-benefit analysis of water and sanitation interventions indicates
that halving the proportion of people without sustainable access to
safe drinking water and basic sanitation by 2015 would not only meet
Millennium Development Goal (MDG) 7c, but would also result in the
following annual improvements:
• avoid more than 5.4 billion cases of diarrhea every year
• save nearly $7 billion in health sector costs
• gain 3.2 million productive work days and 272 billion school days, and
• yield an overall projected return of $5 to $11 for every $1 invested.(12)
Water, sanitation and hygiene interventions save money and save lives.
For those of us lucky enough to live where clean water is plentiful
and a toilet easily accessible, it is difficult to imagine the threat
posed by unsafe water, or the reality of defecating in an open field, or
the disastrous consequences of inappropriate disposal of human waste.
It is difficult even to believe that so many millions of children in the
world waste away from diarrheal disease, either dying or facing a
lifetime of after-effects, simply because the water they drink is
polluted with human waste—that in the minutes it took to read this,
several children died for want of clean water.
But we must face these truths, and talk about toilets, human waste
and dirty water, mosquito larvae and bacteria and parasites, because
only in so doing can we invest our time and energy and money into
improving water, sanitation and hygiene for people around the world,
saving millions of lives and improving health for millions more.
Article by Kristina Talbert-Slagle, Ph.D@P.H. The Yale Journal of Public Health
