Evaluation of Drinking Water Quality in Schools in a District Area in Hanoi, Vietnam – PMC

Physicochemical parameters

pH is classed as one of the most important water quality parameters because it
can affect the disinfection process.26-29 The data in showed that pH
of the water ranged from 6.45 to 8.79 (mean: 7.73). pH is a value to show the
concentration of the hydrogen ion in water. The pH of a neutral solution is 7,
the pH of an alkaline solution is greater than 7, and the pH of an acidic
solution is less than 7. The pH range of safe drinking water mentioned in the
National Technical Regulation on Domestic Water Quality of Vietnam (QCVN01) is
between 6.5 and 8.5, and the desirable limits of WHO for pH is below
8.24,25 Among the tested samples, the pH of 148 samples (96.1%) was
in accordance with the level of WHO and QCVN01, and 6 samples (3.9%) crossed the
permissible guideline values ( ). The pH of drinking water has
no immediate direct effects on human health but has some indirect health effects
by changing other water quality parameters, such as metal solubility and
survival of pathogens. Acidic water can lead to corrosion of metal pipes and
plumbing system. Meanwhile, alkaline water shows disinfection in
water.26-29

Turbidity is another key parameter in drinking water analysis. It is the
cloudiness of water caused by a variety of particles. It is also related to the
content of diseases-causing organisms in water, which may come from soil
runoff.24,30 The standard recommended maximum turbidity limit, set by
WHO and QCVN 01, for drinking water is less than 1 and 2 nephelometric turbidity
units (NTU), respectively, since the appearance of water with a turbidity of
less than this value is usually acceptable to water users.24,25 It does
not have a health based-guideline; nevertheless, microorganisms (bacteria,
viruses and protozoa) are typically attached to particulates. As a consequence,
contamination with bacteria in turbid waters can be occurred and indirectly
effects human health. Moreover, microorganisms can be protected from the effects
of disinfection due to high levels of turbidity, giving rise to a significant
demand for chlorine and reducing the effectiveness of some disinfection
treatments. Therefore, turbidity could be the value to estimate the
microbiological quality and disinfection of water. Low turbidity value due is
often observed in tap water thanks to the good filtration system, which is used
to remove undesired solids and organisms from turbid water.24,30 Out of the
tested samples, only one sample (0.6%) did not meet the standard of WHO or QCVN
with turbidity value of 4.33 NTU ( and ).

The presence of high concentration of heavy metals in drinking water can lead to
an increased risk of many diseases. Thus, the measurement of heavy metals in
drinking water is an important parameter, and evaluation of heavy metals in
drinking water is performed in most studies.19,30-37 Chronic exposure to
arsenic has been shown to cause dermal lesions, neuropathies, cancers of the
skin, bladder and lung and peripheral vascular disease. Iron and manganese may
occur naturally at low levels in the water and may be responsible for taste and
staining problems with the water.36 Manganese is an important trace mineral that is needed by human body in
little amounts for the production of digestive enzymes, absorption of nutrients,
wound healing, bone development and immune-system defenses.36 Negative health effects can be caused by insufficient or excessive intake
of manganese. Human exposure to higher amount of manganese can result in severe
disorders in nervous system, and long term of exposure in its worst condition
can cause permanent neurological effects with symptoms characterized by
Parkinson’s disease.36 Iron (Fe) is an essential element for human health that performs various
function in our body, the most well-known of them is production of protein
hemoglobin, which carry oxygen from lungs to transfer it throughout the body.
Insufficient or excess levels of iron can have negative effect on body
functions. An excess iron in vital organs, increases the risk for liver disease
(cirrhosis, cancer), heart failure, diabetes mellitus, depression,
osteoarthritis, osteoporosis, infertility, hypothyroidism, abdominal pain,
hypogonadism, numerous symptoms and in some cases it becomes cause of premature death.36 In the present study, the values of analysis of heavy metals such as Fe,
As, Mn were also compared with the safe limits set by WHO and QCVN01.24,25 The
concentrations of total iron, manganese, total arsenic measured in drinking
water samples met with the regular limit of WHO and QCVN01guidelines.

Chloride is mainly obtained from the dissolution of salts of hydrochloric acid as
table salt (NaCl), Na2CO3 and added through industrial
waste, sewage, sea water etc. Surface water bodies often have low concentration
of chlorides as compared to ground water.38 According to WHO and QCVN01, concentration of chloride for drinking water
should not exceed 250 mg/L. In this study, chloride ranged from 1.3 to 78.5 mg/L
with an average value of 14.94 mg/L. Thus, low concentration of chloride was
observed in the tested samples ( ). Sulfate concentration in
natural water ranges from a few to a several hundred mg/L, but no major negative
impact of sulfate on human health is reported. Sulfate concentration ranged from
1.3 to 27.1 mg/L with an average value of 9.45 mg/L. Sulfate drinking water
standards of QCVN01 and WHO have established 250 and 500 mg/L, respectively.
Therefore, all water samples met the permissible limits.

The water hardness (CaCO3) is dependent on some major anions and
cations, such as bicarbonate, sulfate, chloride, calcium and magnesium. Water
with CaCO3 concentration range from 0 to 75 mg/L CaCO3 is
considered as soft; range from 75 to 150 mg/L, moderately hard; range from 150
to 300mg/L, hard; and greater than 300 mg/L, very hard water. It is known that
the water hardness induces no effects in human health, but high hardness can
cause problems for daily human uses.39 The total hardness values (CaCO3) of the tested samples ranged
from 0 to 220 mg/L and a mean value of 67.6 mg/L, which met the regular limit of
QCVN01 (<300 mg/L CaCO3).

Nitrate (NO3) and nitrite (NO2) are ions found in the
environment. Both are products of the oxidation of nitrogen, as part of the
cycle required by all living systems for the production of complex organic
molecules, such as enzymes and other proteins. Nitrate is the stable form of
oxidized nitrogen. However, under anaerobic conditions and in the presence of a
carbon source, microbial action can reduce nitrate to nitrite, which is
relatively unstable and moderately reactive. Water supplies contaminated with
nitrate is often due to agricultural activities that involve the use of
fertilizers. The health effects of nitrate and nitrite come from its ability to
cause methaemoglobinaemia in humans, especially in children fed with milk or
water containing high concentrations of this chemicals.40-42 This study showed that the
nitrate level in all the samples, which ranged from 0.1 to 40 mg/L with an
average value of 3.9 mg/L, was lower than the maximum recommended limit
(50 mg/L) of WHO and QCVN01. However, 5 samples (3.2%) exceeded the regular
limit of nitrite in drinking water (⩽3 mg/L) as shown in .

The permanganate index is a conventional measure of the contamination by organic
and oxidizable inorganic matter in a water sample.24,25 The permanganate index of
water samples ranged from 0.8 to 14.4 mg/L. An index of less than 2 mg/L is
accepted by the standard of QCVN01. The data showed that 10 samples (6.5%)
crossed the permissible guideline values as shown in , suggesting possible
contamination by organic matter in the samples. Ammonia in water exists either
in the form of un-ionized ammonia or the ammonium ion. The reported value in
studies is usually the sum of both forms and reported as total ammonia or
simply-ammonia. pH value strongly effects the relative proportion of the two
forms present in water. When pH is high, un-ionized ammonia is the toxic form
and predominates. On the other hand, when pH is low, the
NH4+ion is relatively non-toxic and predominates. In
general, when pH is less than 8.0 pH units less than 10% of ammonia is in the
toxic form, and this proportion increases dramatically as pH
increases.24,25