QUALITY STANDARD

Introduction

The Objective of Water Works Management is to ensure that the water supplied is free from pathogenic organisms, clear, palatable and free from undesirable taste and odour, of reasonable temperature, neither corrosive nor scale forming and free from minerals which could produce undesirable physiological effects. The establishment of minimum standards of quality for public water supply is of fundamental importance in achieving this objective. Standards of quality form the yardstick within which the quality control of any public water supply has to be accessed.

Sanitary inspections are intended to provide a range of information and to locate potential problems. The inspections allow for an overall appraisal of many factors associated with a power supply system including the water work, and the distribution system. Moreover such an appraisal may later be verified and confirmed by microbiological analysis, which will indicate the severity of the problem. Sanitary inspections thus provide a direct method of pinpointing possible problems and source of contamination. They are also important in the prevention and control of potentially hazardous conditions, including epidemic of water borne diseases. The data obtained may identify failures, anomalies, operator errors and any deviations from normal that may affect the production and distribution of safe drinking water. When the inspections are properly carried out at appropriate regular intervals and where the inspector has the knowledge necessary to detect problems and suggest technical solutions, the production of good quality water is assured.

The evolution of standards for the quality control of public water supplies has to take into account the limitations imposed by local factors in the several regions of the country. The Environment Hygiene Committee (1949) recommended that the objective of a public water supply should be to supply water “that is absolutely free from risks of transmitting diseases, is pleasing to the senses and is suitable for culinary and laundering purpose” and added that “freedom from risks is comparatively more important than physical appearance or hardness” and that safety is an obligatory standard and physical and chemical qualities are optional within a range .These observations are relevant in the development of a country-wide programs of protected water supply systems for communities big and small, making use of the available water resources in the different regions, with a wide variation in their physical, chemical and aesthetic qualities, that can be achieved by communities in due course within the limits of their financial resources. The immediate need is for minimum standards, consistent with the safety of public water supplies. Considering the standards prescribed in the earlier Manual and further development in the international standardization and the conditions in the country, the following guidelines are recommended.

Physical and Chemical Quality of Drinking Water

The physical and chemical quality of drinking water should be in accordance with the recommended guidelines presented in table 2.2

TABLE 2.2

RECOMMENDED GUIDELINES FOR PHYSICAL AND CHEMICAL PARAMETERS

If there are 250 mg/l of sulphates, Mg content can be increased to a maximum of 125mg/l with the reduction of sulphates at the rate of 1unit per every 2.5 units of sulphates.

NOTES:

* The figures indicated under the column ‘Acceptable’ are the limits upto which water is generally acceptable to the consumers.

** Figures in excess of those mentioned under ‘Acceptable’ render the water not acceptable, but still may be tolerated in the absence of an alternative and better source but upto the limits indicated under column “Cause for Rejection” above which the sources will have to be rejected.

+ It is possible that some mine and spring waters may exceed these radio activity limits and in such cases it is necessary to analyze the individual radio-nuclides in order to assess the acceptability or otherwise for public consumption.

b) Bacteriological Guidelines

TABLE 2.3

BACTERIALOGICAL QUALITY OF DRINKING WATER

Source: WHO guidelines for Drinking Water Quality Vol.1 – 1993.

• Immediate investigative action must be taken if either E.coli or total coliform bacteria are detected. The minimum action in the case of total coliform bacteria is repeat sampling; if these bacteria are detected in the repeat sample, the cause must be determined by immediate further investigation.
• Although E.coli is the more precise indicator of faecal pollution, the count of thermotolerant coliform bacteria is an acceptable alternative. If necessary, proper confirmatory test must be carried out. Total coliform bacteria are not acceptable indicators of the sanitary quality of rural water supplies, particularly in tropical areas where many bacteria of no sanitary significance occur in almost all untreated supplies.
• it is recognized that, in the great majority of rural water supplies in developing countries, faecal contamination is widespread. Under these conditions, the national surveillance agency should set medium term targets for progressive improvement of water supplies, as recommended in volume 3 of W.H.O. guidelines for drinking water supply 1993.

c) Virological Quality

Drinking water must essentially be free of human enteroviruses to ensure negligible risk of transmitting viral infection. Any drinking water supply subject to faecal contamination presents a risk of a viral disease to consumers. Two approaches can be used to ensure that the risk of viral infection is kept to a minimum: providing drinking water from a source verified free of faecal contamination or adequately treating faecally contaminated water to reduce enteroviruses to a negligible level.

Virological studies have shown that drinking water treatment can considerably reduce the levels of viruses but may not eliminate them completely from very large volumes of water. Virological, epidemiological, and risk analysis are providing important information, although it is still insufficient for deriving quantitative and direct virological criteria. Such criteria can not be recommended for routine use because of the cost, complexity, and lengthy nature of virological analysis, and the fact that they can not detect the most relevant viruses.

The guidelines criteria shown in table 2.4 are based upon the likely viral content of source waters and the degree of treatment necessary to ensure that even very large volumes of drinking water have negligible risk of containing viruses.

Ground water obtained from a protected source and documented to be free from faecal contamination from its zone of influence, the well, pumps, and delivery system can be assumed to be virus free. However, when such water is distributed, it is desirable that it is disinfected, and that a residual level of disinfectant is maintained in the distribution system to guard against contamination.

TABLE 2.4

RECOMMENDED TREATMENT FOR DIFFERENT WATER SOURCES TO PRODUCE WATER WITH NEGLIGIBLE VIRUS RISK*

a. For all sources, the median value of turbidity before terminal disinfection must not exceed 1 nephelometric turbidity unit (NTU) and must not exceed 5 (NTU) in single sample.

Terminal disinfection must produce a residual concentration of free chloride of =0.5 mg/litre after at least 30 minutes of contract in water at pH < or must be shown to be an equivalent disinfection process in terms of the degree of enterovirus inactivation (>99.99%).

Filtration must be slow sand filtration or rapid filtration (sand, dual, or mixed media) preceded by adequate coagulation-flocculation (with sedimentation or floatation). Diatomaceous earth filtration or filtration process demonstrated to be equivalent for virus reduction can also be used. The degree of virus reduction must be >90%.

Additional treatment may consist of slow sand filtration, ozonation with granular activated carbon adsorption, or any other process demonstrated to achieve > 99% enterovirus reduction.

b. Disinfection should be used if monitoring has shown the presence of E.coli or thermotolerant coliform bacteria.

SOURCE: W.H.O. guidelines for drinking water quality-1993 .