| Drinking Water Quality |
| Drinking water quality is considered the quality or state of your drinking water, and can be evaluated at many levels. To help with this drinking water evaluation process, some general guidelines have been established as a basis for the development of national drinking water standards. If properly implemented, these national drinking water standards will ensure the safety of drinking water supplies through the elimination, or reduction to a minimum concentration, of constituents of drinking water that are known to be hazardous to health. It must be emphasized that the drinking water guideline values recommended are not mandatory limits. In order to define such limits, it is necessary to consider the drinking water guideline values in the context of local or national environmental, social, economic, and cultural conditions. The main reason for not promoting the adoption of international standards for drinking water quality is the advantage provided by the use of a risk-benefit approach (qualitative or quantitative) to the establishment of national standards and regulations. This approach should lead to drinking water standards and regulations that can be readily implemented and enforced. For example, the adoption of drinking water standards that are too stringent could limit the availability of drinking water supplies that meet those standards – a significant consideration in regions of water shortage. The drinking water standards that individual countries will develop can thus be influenced by national priorities and economic factors. However, considerations of policy and convenience must never be allowed to endanger public health, and the implementation of drinking water standards and regulations will require suitable facilities and expertise as well as the appropriate legislative framework. The judgment of safety – or what is an acceptable level of risk in particular circumstances – is a matter in which society as a whole has a role to play. The final judgment as to whether the benefit resulting from the adoption of any of the guideline values given here as standards justify the cost is for each country to decide. What must be emphasized is that the guideline values have a degree of flexibility and enable a judgment to be made regarding the provision of drinking water of acceptable quality. Water is essential to sustain life, and a satisfactory supply must be made available to consumers. Every effort should be made to achieve drinking water quality as high as practicable. Protection of drinking water supplies from contamination is the first line of defense. Source protection is almost invariably the best method of ensuring safe drinking water and is to be preferred to treating a contaminated water supply to render it suitable for consumption. Once a potentially hazardous drinking water situation has been recognized, however, the risk to health, the availability of alternative sources, and the availability of suitable remedial measures must be considered so that a decision can be made about the acceptability of the drinking water supply. As far as possible, drinking water sources must be protected from contamination by human and animal waste, which can contain a variety of bacterial, viral, and protozoan pathogens and helminth parasites. Failure to provide adequate protection and effective treatment will expose the community to the risk of outbreaks of intestinal and other infectious diseases. Those at greatest risk of waterborne disease are infants and young children, people who are debilitated or living under unsanitary conditions, the sick, and the elderly. For these people, infective doses are significantly lower than for the general adult population. The potential consequences of microbial contamination are such that its control must always be of paramount importance and must never be compromised. The assessment of the risks associated with variations in microbial quality is difficult and controversial because of insufficient epidemiological evidence, the number of factors involved, and the changing interrelationships between these factors. In general terms, the greatest microbial risks are associated with ingestion of drinking water that is contaminated with human and animal excreta. Microbial risk can never be entirely eliminated, because the diseases that are waterborne may also be transmitted by person-to-person contact, aerosols, and food intake; thus, a reservoir of cases and carriers is maintained. Provision of a safe water supply in these circumstances will reduce the chances of spread by these other routes. Waterborne outbreaks are particularly to be avoided because of their capacity to result in the simultaneous infection of a high proportion of the community. The health risk due to toxic chemicals in drinking water differs from that caused by microbiological contaminants. There are few chemical constituents of water that can lead to acute health problems except through massive accidental contamination of a supply. Moreover, experience shows that, in such incidents, the water usually becomes undrinkable owing to unacceptable taste, odor, and appearance. The fact that chemical contaminants are not normally associated with acute effects places them in a lower priority category than microbial contaminants, the effects of which are usually acute and widespread. Indeed, it can be argued that chemical standards for drinking water are of secondary consideration in a supply subject to severe bacterial contamination. The problems associated with chemical constituents of drinking water arise primarily from their ability to cause adverse health effects after prolonged periods of exposure; of particular concern are contaminants that have cumulative toxic properties, such as heavy metals, and substances that are carcinogenic. It should be noted that the use of chemical disinfectants in water treatment usually results in the formation of chemical by-products, some of which are potentially hazardous. However, the risks to health from these by-products are extremely small in comparison with the risks associated with inadequate disinfection, and it is important that disinfection should not be compromised in attempting to control such by-products. The radiological health risk associated with the presence of naturally occurring radionuclides in drinking water should also be taken into consideration, although the contribution of drinking water to total ambient exposure to these radionuclides is very small under normal circumstances. The guideline values recommended in this volume do not apply to water supplies contaminated during emergencies arising from accidental releases of radioactive substances to the environment. In assessing the quality of drinking water, the consumer relies principally upon his or her senses. Water constituents may affect the appearance, odor, or taste of the water, and the consumer will evaluate the quality and acceptability of the water on the basis of these criteria. Water that is highly turbid, is highly colored, or has an objectionable taste or odor may be regarded by consumers as unsafe and may be rejected for drinking purposes. It is therefore vital to maintain a drinking water quality that is acceptable to the consumer, although the absence of any adverse sensory effects does not guarantee the safety of the water. Countries developing national drinking-water limits or standards should carefully evaluate the costs and benefits associated with the control of aesthetic and organoleptic quality. Enforceable standards are sometimes set for contaminants directly related to health, whereas recommendations only are made for aesthetic and organoleptic characteristics. For countries with severely limited resources, it is even more important to establish priorities, and priorities should be set only after considering the impact on health in each case. This approach does not underestimate the importance of the aesthetic quality of drinking water. Source water that is aesthetically unsatisfactory may discourage the consumer from using an otherwise safe supply. Furthermore, taste, odor, and color may be the first indication of potential health hazards. Many parameters must be taken into consideration in the assessment of water quality, such as source protection, treatment efficiency and reliability, and protection of the distribution network (e.g., corrosion control). The costs associated with water quality surveillance and control must also be carefully evaluated before developing national standards. Home Page | FAQs | Glossary | Contact Us |