DRINKING WATER QUALITY
S.K.Panda
Director(HDD), ISO, CWC
801(F)-North, Sewa Bhawan,
R.K.Puram, New Delhi-110066
Synopsis: Earlier BIS standards were followed and found that the water quality at some CWC sites had a little bit variation from the standards. In this paper the USEPA standards were followed. The water quality data of all the CWC sites of various river basisns were compared and it was found that there was no variation from USEPA standards.The water quality parameters at all CWC sites in INDIA are within the prescribed USPEA limits.
1. INTRODUCTION
Domestic water supply is widely acknowledged as a key element in the fight against poverty and disease. Adequate drinking water supply is rightly seen as essential to human well being. From watering livestock to brewing beer, in rural, urban and semi urban environments, water is crucial enabler of economic activity – particularly for women and the poor.
Adequate knowledge of the existing nature, magnitude and sources of various pollutional loads in water bodies is necessary for any national formulation of water quality management and water-pollution control policies and programmes. For a vast country like India with varying meteorological, hydrological, and developmental conditions, the policies and programmes related to water quality management can be made effective only if taken up on a river-basin-wise approach. In the present study we will cover all river basins.
While proposing any policy and programme formulation for water pollution control, it is imperative to take into account certain predominant features of the country within which such programmes are to be implemented. Poverty, ignorance and lack of adequate socio-economic development are three abominable social realities that still continue to dominate the community life in India. The use of water courses by people, by and large, can not be viewed in isolation ignoring these factors. Thus, in any water quality improvement/protection programme, it must be recognized that such a programme has to be pursued amidst the overriding limitations prevalent in Indian communities, which are not likely to change radically. Over and above this, rivers have always been regarded in India from ancient days, as sacred water bodies which purge away sins, and being observed by such faith, people bath in these rivers with very little concern about whether the rivers are polluted or not.
Water is a prime necessity for human survival and for growth of agriculture as well as for industrial development. Effective management of water resource, monitoring and control of its quality are becoming increasing important for sustainable development and human welfare. Pollution of water has become a universal phenomena in present day world and for maintaining water quality at acceptable levels, Environmental Protection Act also includes, as one of its objectives, protection of water from pollution. Now-a-days, greater emphasis is also being given to water quality because of concern of environmentalist. Degradation of water quality is not only caused by increasing inflow of domestic and industrial waste water into water course, but also from the abstraction of water from rivers rendering them dry or with meager flow leading to concentration of pollution.
Some people are more vulnerable to contaminants in drinking water than the general population. People undergoing chemotherapy or living with HIV/AIDS, transplant patients, children and infants, the frail elderly, and pregnant women and their fetuses can be particularly at risk for infections. If someone has special health care needs, he should take additional precautions with his drinking water. Cost of making water safe continues to rise.
2. Common Sources of Pollution
a) Naturally occurring: Microorganisms (wild life and soils), radionuclides (underlying rock), nitrates and nitrites (nitrogen compounds in the soil), heavy metals (underground rocks containing arsenic, cadmium, chromium, lead and selenium), and fluoride.
b) Human Activities: Bacteria and nitrates, human and animal wastes –(septic tanks and large farms), heavy metals (mining construction, older fruit orchards), fertilizers and pesticides, industrial products and wastes, household wastes, lead and copper (household plumbing material) and water treatment chemicals (waste water treatment plants)
Actual events of drinking water contamination are rare and typically don’t occur at levels likely to pose health problems. However, as development in our modern society increases, these are growing number of activities that can contaminate our drinking water. Improperly disposed of chemicals, animal and human wastes, wastes injected underground and naturally occurring substances have the potential to contaminate drinking water. Likewise, drinking water that is not properly treated or disinfected, or that travels through an improperly maintained distribution system, may also pose a health risk.
Water should be boiled to prevent microbial contamination while it should not be boiled for nitrate fertilizer and lead contaminations.
There is no such thing as naturally pure water. In nature, all water contains some impurities. As water flows in streams, sits in lakes, and filters through layers of soil and rock in the ground, it dissolves or absorbs the substances it touches. Some of these substances are harmless. In fact some people prefer mineral water precisely because minerals give it an appealing taste. However, at certain levels, minerals, just like man-made chemicals, are considered contaminants that can make water unpalatable or even unsafe.
Some contaminants come from erosion of natural rock formations. Other contaminants are substances discharged from factories, applied to farm lands, or used by consumers in their homes and yards. Sources of contaminants might be in the neighbourhood or might be many miles away. The local water quality report tells which contaminants are there in the drinking water, the levels at which they were found, and the actual or likely source of each contaminant.
Some ground water systems have established well head protection programs to prevent substances from contaminating the wells. Similarly, some surface water systems protect the watershed around their reservoir to prevent contamination. Right now, states and water suppliers are working systematically to assess every source of drinking water and to identify potential sources of contaminations. This process will help communities to protect their drinking water supplies from contamination.
Environmental Protection Agency (EPA) has set standards for more than 80 contaminants that may occur in drinking water and pose a risk to human health. EPA sets these standards to protect the health of every body, including vulnerable groups according to the health effects that they cause e.g. acute or chronic health effect from compounds in drinking water.
a) Acute effects occur within hours or days of the time that a person consumes a contaminant. People can suffer acute health effects from almost any contaminant if they are exposed to extra ordinarily high levels (as in the case of a spill). In drinking water, microbes, such as bacteria and viruses, are the contaminants with the greatest chance of reaching levels high enough to cause acute health effects. Most people’s bodies can fight off these microbial contaminants the way they fight off germs, and these acute contaminants typically don’t have permanent effects. Nonetheless, when high enough levels occur,they can make people ill, and can be dangerous or deadly for a person whose immune system is already weak due to HIV/AIDS, chemotherapy, steroid use, or another reason.
b) Chronic effects occur after people consume a contaminant at levels over EPA’s safety standards for many years. The drinking water contaminant that can have chronic effects are chemicals (such as disinfection by products, solvents, and pesticides), radio nuclides (such as radium), and minerals (such as arsenic). Examples of these chronic effects include cancer, liver or kidney problems, or reproductive difficulties.
3. Treatment of Drinking Water
The amount and type of treatment applied varies with the source and quality of water. Generally, surface water systems require more treatment than ground water systems because they are directly exposed to the atmosphere and runoff from rain and melting snow.
Water suppliers use a variety of treatment processes to remove contaminants from drinking water. These individual processes can be arranged in a “treatment train” ( a series of processes applied in a sequence ). The most commonly used processes include coagulation (flocculation and sedimentation), filtration and disinfection. Some water systems also use ion exchange and absorption Water utilities select the treatment combination most appropriate to treat the contaminants found in the source water of that particular system.
All sources of drinking water contain some naturally occurring contaminants. At low levels, these contaminants generally are not harmful in our drinking water. Removing all contaminants would be extremely expensive and in most cases, would not provide increased protection of public health. A few naturally occurring minerals may actually improve the taste of drinking water and may even have nutritional value at low levels.
a) Coagulation (Flocculation and sedimentation)
Flocculation:- This step removes dirt and other particles suspended in the water. Alum and iron salts or synthetic organic polymers are added to the water to form tiny sticky particles called “floc”, which attract the dirt particles.
Sedimentation:- The flocculated particles then settle naturally out of the water.
b) Filtration:- Many water treatment facilities use filtration to remove all particles from the water. Those particles include clays and silts, natural organic matter, precipitates from other treatment processes in the facility, iron and manganese and micro-organisms. Filtration clarifies the water and enhances the effectiveness of disinfection. Water passes through charcoal, sand and gravel layers in a filtration tank.
c) Disinfection:- Disinfection of drinking water is considered to be one of the major public health advances of the 20th century. Water is often disinfected before it enters the distribution system to ensure that dangerous microbial contaminants are killed. Chlorine, chlorinates, or chlorine dioxides are most often used because they are very effective disinfectants and residual concentrations can be maintained in the water system. However, sometimes the disinfectants themselves can react with naturally occurring materials in the waster to form unintended byproducts which may pose health risks. EPA recognizes the importance of removing microbial contaminants while simultaneously protecting the public from disinfection byproducts and has developed regulations to limit the presence of these byproducts.
Home treatment of water:
A home water treatment unit can improve water’s taste or provide a factor of safety for those people more vulnerable to water-borne disease. There are different options for home treatment systems. Point of Use (POU) system treat water at a single tap. Point of Entry (POE) system treat water used throughout the house. POU systems can be installed in various places in the home. POE systems are installed where the water line enters the house.
POU and POE devices are based on various contaminant removal technologies. Filtration, ion exchange, reverse osmoisis, and distillation are some of the treatment methods used. All POU and POE treatment units need maintenance to operate effectively. If they are not maintained properly, contaminants may accumulate in the units and actually make water worse.
The table below shows the treatment device, water treatment and limitations.
|
|
Treatment Device |
What it does to water |
Limitations |
|
1. |
Activated Carbon Filter |
§ Absorbs organic contaminants that cause taste and odor problems. § Some designs remove chlorination byproducts. § Some types remove cleaning solvents and pesticides. |
§ Is not efficient in removing metals such as lead & copper. § Does not remove nitrate, bacteria or dissolved minerals. |
|
2. |
Ion exchange unit with activated alumina. |
§ Removes minerals like calcium & magnesium that makes water ‘hard’. § Some design remove radium & barium. § Removes fluride & arsenate. |
§ If water has oxidized iron or iron bacteria, the ion-exchange resin will become coated or clogged and loose its softening ability. |
|
3. |
Reverse Osmosis unit with carbon |
§ Removes nitrates, sodium, other dissolved inorganic and organic compounds. § Removes foul tastes, smells or colors. § May also reduce the level of some pesticides, dioxins, chloroform and petrochemicals. |
§ Does not remove all inorganic and organic contaminants. |
|
4. |
Distillation Unit |
§ Removes nitrates, bacteria, sodium, hardness, dissolved solids, most organic compounds, heavy metals and radio nuclides. § Kills bacteria. |
§ Doesnot remove some volatile organic contaminants, certain pesticides & volatile solvents. § Bacteria may recolonise on the cooling coils during inactive periods.
|
4. Protection of Ground Water Supply.
1. The exposed parts of the well must be periodically inspected such as: cracked, corroded or damaged well casing, broken or missing well cap, settling and cracking of surface seals.
2. The area around the well must be sloped to drain surface run-off away from the well.
3. A well cap or sanitary seal must be installed to prevent unauthorized use of, entry into the well.
4. Drinking water wells must be disinfected at least once every year with bleach or hypochlorite granules.
5. The well must be tested once a year for coliform bacteria, nitrates and other constituents of concern.
6. Accurate record must be kept for any well maintenance such as disinfection or sediment removal that may require the use of chemicals in the well.
7. A certified well driller must be hired for any new well construction, modification or abandonment and closure.
8. Mixing of using pesticides, fertilizers, herbicides, degreasers, fuels and other pollutants must be avoided near the well.
9. Wastes should not be disposed in dry wells or in abandoned wells.
10. Well casing should not be cut off below the land surface .
11. Septic systems must be pumped and inspected as often as recommended by the local health department.
12. Hazardous materials must not be disposed in a septic system.
5. WHO Guidelines for Drinking Water Quality (GDWQ)
In 1950, the requirements for safe and potable water supplies became particularly pertinent with the great increase in travel, especially global air travel. It became apparent that the traveler must be provided with potable drinking water. In 1953, WHO distributed a questionnaire to all member states to assess the status of water treatment plants and their production of acceptable water quality. The replies to the questionnaire clearly indicated the magnitude of the problem and the need for WHO to establish drinking water standards. Following a series of expert consultations culminating in a meeting in 1956 in Geneva the International Standards for drinking water were published in 1958. In this instance, the term “standards” was used to be applied to the suggested criteria of water quality (WHO 1958). The 1958 International Standards became to be widely used as a reference in the development of local national standards and as a basis for improved water treatment practices.
Some countries adopted the International standards as the official and legal standards of water quality while other countries developed national standards based in part or in whole on the International Standards Increasing knowledge of the nature and effect of various contaminants and improved techniques for identifying and determining their concentrations have led to a demand for further revision of the recommendations. Accordingly, the International Standards for drinking water were revised in 1963 and 1971 (WHO 1958, 1963, 1971). The International Standards had been in existence for over a decade until they were superseded by the WHO Guidelines for Drinking Water Quality (GDWQ) in 1987. While it was recognized that it might not be possible by a number of member states to attain all the recommended guideline levels, it was anticipated that the member states would develop water quality standards as close as possible to these guidelines in the endeavour to protect public health.
The philosophy and content of the WHO Guidelines constituted a drastic departure from the previous International Standards. The revised guidelines were published in 3 Volumes including criteria monographs prepared for each substance or contaminant listed in the guidelines (WHO 1984,1985). The second edition of the GDWQ Volume 1 was published in 1993 followed by Volume 2 in 1996 and Volume 3 in 1997. The International Programme on Chemical Safety(IPCS) provided major input to the health risk assessments of chemicals in drinking water. In case of compounds considered to be genotoxic and carcinogenic, the International Agency for Research on Cancer (IARC) classification of Carcinogenic compound was taken into consideration and guideline values were established using a mathematical model, usually the linearized multistage extrapolation model.
The guideline values are presented as the concentration in drinking water associated with an estimated excess lifetime cancer risk of 10-5 (one additional cancer case per 100000 of the population ingesting drinking water containing the substance at the guideline value for 70 years). In cases in which the concentration in drinking water associated with a 10-5 excess lifetime cancel risk was not practical, because of inadequate analytical methodology, a provisional guideline value was set at a practicable level and the estimated cancer risk was presented (WHO 1993). A continuing process of updating guideline values was established with a number of chemical substances and microbiological agents subject to periodic evaluation . Addenda containing these evaluations were issued in 1998 for volumes 1 & 2 (WHO 1998).
Purpose of GDWQ
In GDWQ, it is often emphasized that the guideline values recommended are not mandatory limits. In order to define such limits, it is necessary to consider the guideline values in the context of local or national environmental, social, economic and cultural adoption of international standards for drinking water quality is the advantage provided by the use of a risk benefit approach (gualitative & quantitative) to the establishment of national standards and regulations. The final judgement as to whether the benefit resulting from the adoption of any guideline value as standard justifies the cost is for each country to decide (WHO 1993)
Risk assessment by Multistage Model
Multistage model is one of the mathematical models, which is most frequently used in regulatory process. It was also applied in the 1988 risk assessment for arsenic in drinking water done by USEPA using the data of an epidemiological study by Tseng et al in 1968. This model is based on the concept that a tumour develops from a single cell in an organ as a result of a number of biological events or stages (e.g. mutation)that occur in a prescribed order. According to this model, the probability of developing tumours, P(d), is
P(d) = 1-exp[-(a+q1d+q2d2+q3d3+….+qmdm)]
Where the parameter m is the n umber of stages, a is the background tumour rate and the q’s are the values that maximize the likelihood of observing the experimental results. In practice, the a, the q and the m are estimated from the data. Some of the q’s may be zero but none can be negative. When the unknown values of the multistage model parameters are replaced by their MLE’s, the resulting model estimates what the risk is most likely to be in the experimental situation. At low doses, the dose-response relationship is thus approximately linear. This model will fit almost any observed data set as long as the dose-response curve is not marked by concave downward at low responses. It is important to note that quantitative risk estimates may give an impression of accuracy which in fact they do not have. In general, the risk assessment values for carcinogens are at best, “order of magnitude” estimates.
It should be emphasized that the guideline values for carcinogenic substances have been computed from hypothetical mathematical models that cannot be verified experimentally and that the values should be interpreted differently than TDI based values because of the lack of precision of the models. At best, these values must be regarded as rough estimates of cancer risk. However, the models used are conservative and probably err on the side of caution. Modernate short term exposure to levels exceeding the guideline value for carcinogens does not significantly affect the risk.
6. Drinking Water Quality of All Basins.
At various Central Water Commission sites of all major River Basins, the water quality analysis have been performed. Comparison has been made with USEPA standards of 2001 at Annexure-1. No deviation from USEPA standards was found in all cases. At all CWC sites in India, the drinking water quality is within the limits of USEPA standards.
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