Further to your article "Tests reveal tap water 'drinkable'" (Nov. 19-Dec.
2) by Maeve Donelan.
We are afraid that rather than providing new and useful information to your readers,
your article can contribute to unjustified complacency or alarm. It also contained
serious errors and a number of omissions.
Water that is bacteriologically "safe" is not necessarily fit for drinking
from a chemical perspective and vice versa. Micro biological and chemical aspects
of water quality are important from a health perspective and a water can fail quality
tests in either category.
The most common and widespread danger associated with drinking water is contamination,
either directly or indirectly, by sewage, human or animal excrement, or other wastes.
Fecal pollution of drinking water may introduce a variety of pathogens (bacteria,
protozoa, helminths, etc) into the water, and the use of this water for drinking
or food preparation may cause further cases of infection.
In developing countries, it is usually these infectious water-related diseases which
are of prime importance, not the non-infectious diseases related to some chemical
property of the water.
The recognition that microbial infection can be water-borne has led to simple methods
for the routine examination of drinking water. The micro biological quality of drinking
water is typically expressed in terms of the concentration and frequency of occurrence
of particular species of bacteria.
The detection and enumeration of all pathogens that may be present in water is
far too complex and time consuming to carry out on a routine basis and it is therefore
normal practice to detect and enumerate only what are called "indicator bacteria".
These are bacteria that are always excreted in large numbers by man, whether sick
The presence of indicator bacteria in water is therefore indicative of fecal contamination
of that water. If a sample of water is fecally contaminated, it may contain any pathogen
which is being excreted by the population causing the fecal pollution. Fecal contamination
in a water is thus taken to indicate that water may constitute a health hazard.
The most commonly used indicator bacteria are the coliforms, and water is tested
either for the presence of the total coliform group (chlorinated supplies), or for
the presence of exclusively fecal coliforms (mainly comprising coli) only (unchlorinated
The micro biological quality of a water is then expressed as the number of total
coliforms, or fecal coliforms, per 100ml of water. WHO has established guidelines
as to which concentrations should be considered acceptable in given circumstances
(ranging from 0-10 coliform organisms per 100ml depending on the type of supply).
Thus when your article quotes Dr. Chea as saying that "...(the water) contained
a high level of bacteria (between 2.10 and 2.15 mg of organic matter per litre)"
the author has her date mixed up.
Organic load is usually only determined for sewage and waste waters, not for drinking
water. It certainly is no direct indication of bacterial pollution. Besides that,
it is impossible to determine the actual amount of organic matter present in a water.
Organic load is usually expressed as the Oxygen Demand (OD) of a water, in mg per
litre, with a high OD corresponding to a high organic load.
Nothing in your article suggests that micro biological tests were carried out on
the various water samples, which seems to us a serious omission.
To state that "Water drawn from the Tonle Bassac in front of the Royal Palace
also appeared to pass safety tests" is most misleading. Even if bacterial tests
were carried out on the river water, results of such tests should be interpreted
with caution, since turbid waters with many other bacteria present (such as most
tropical rivers) are prone to give false negative results.
Chemical (and physical) water quality standards are commonly laid down for treated
water. For untreated water supplies. chemical water quality standards are generally
Of most importance from a public health point of view are the inorganic constituents
of a water (organics, such as pesticides, are important as well, but intake in food
is of much more importance here than intake in water).
Tests carried out for the Phnom Penh Post seemed to be focused on the presence of
Nitrate and nitrite should always be considered together, because conversion from
one form to the other occurs in the environment. Concentrations in water are expressed
as mg per litre of nitrate-nitrogen (nitrate-N) and nitrite-nitrogen (nitrite-N).
The first thing to note is that nitrate and nitrite are widespread in the environment;
they are found in most foods, in the atmosphere, and in many water sources.
Levels of nitrate in water are typically below 5 mg of nitrate-N per litre (although
concentrations of 20 times that can occasionally be found) with the levels of nitrite
almost invariably very much lower.
Most of the higher levels of nitrate are found in ground water; in surface water
they tend to get depleted by aquatic plants. Having said that, marked seasonal variations
can occur in concentration in rivers, and high levels may occur especially after
heavy rainfall (eg because of runoff from agricultural areas using fertilizer).
Conventional water treatment and disinfection methods do not affect the levels
of nitrate in a water, but nitrite levels are much reduced through oxidation and
Surface or ground waters which receive organic pollution from sewage discharges or
on-site sanitation systems (such as pit latrines) may show high nitrate levels. A
rising nitrate level in ground water is a warning sign of continuing pollution. Although
boiling water will kill all bacteria, it is likely to increase nitrate concentration
further because of evaporation.
Nitrate concentrations over 20 mg/l in drinking water are potentially hazardous to
health in two ways. The nitrates are reduced in the body to nitrites and can cause
a serious blood condition in bottle-fed infants known as methaemoglobinaemia (also
called infantile cyanosis or "blue baby syndrome"), particularly if the
diet is low in vitamin C.
High nitrate concentrations have also been implicated in the causation of gastric
The adverse effects of nitrate invariably involve its reduction to nitrite as a preliminary
step. Hence the ingestion of nitrite leads to a more rapid onset of clinical effects,
and nitrite concentrations should be lower than that of nitrate.
WHO recommends a guideline value of 10 mg/l of nitrate and, although no guideline
value is set for nitrite, it observes that where water is correctly treated, the
nitrite nitrogen level should be considerably lower than 1 mg/l .
The results published in the article are thus incomplete; drawing conclusions from
nitrite levels in a water without considering nitrate levels is useless. It is true
that very high nitrite levels are usually associated with water of unsatisfactory
micro biological quality but the levels of nitrite found are quite low.
Unless Dr Chea Chay has had access to test results that were not reported, classifying
the water as "very toxic" is baseless. It is to be regretted that Dr Chea
Chay overlooked the implications of high nitrate concentrations in water; cases of
serious illness and death in bottle-fed infants are well documented.
All in all, we are afraid that rather than providing new and useful information to
your readers, your article can contribute to unjustified complacency (the river water
passed safety tests) or alarm (certain bottled waters are toxic).
Charged with the responsibility for water supplies in Cambodia, the Department of
Hydrology shares your concern about the water supply situation in the country. [This
month,] a first group of department staff will be trained in carrying out bacteriological
and chemical tests on public water supplies.
Building up a picture of the current situation and trends over the years will
enable the department to formulate sound water development strategies. No one is
served, however, with incomplete or misinterpreted data.
We hope that in the next issue of the Phnom Penh Post you can publish aditional results
justifying your conclusions, or write a clarification based on the background information
in this letter. We would be happy to assist you with interpreting the results of
the tests that were carried out on behalf of the Phnom Penh Post.
Veng Sakhon, vice chief, Water Management Office, Department of Health, and Jan-Willem
Rosenboom, rural water supply advisor (Oxfam).