Establishing National Drinking-Water Standards
Session Objectives
· To describe the
need to establish national water quality standards.
· To examine the role of the
Guidelines as the basis for the development of national standards.
· To discuss the factors to be
considered when setting national standards.
· To identify the process of
national standards development.
· To identify priorities for
national drinking-water quality standards.
· To discuss the establishment
of national drinking-water quality standards in the context of legal
frameworks.
Introduction
The primary aim of setting national drinking-water standards is
the protection of public health and thus the elimination, or reduction to a
minimum, of constituents of water that are known to be hazardous to the health
of the community. However, standards achieve nothing unless they can be
implemented and enforced, and this requires relatively expensive facilities and
expertise as well as the appropriate legislative framework.
As reflected in the title, the Guidelines for Drinking-Water
Quality are intended to be used as a basis for the development of national
standards by the appropriate authorities in Member States. It must be emphasised
that the recommended guideline values 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
conditions.
The main reason for not promoting the adoption of international
standards for drinking-water quality is the necessity of using a risk-benefit
approach (qualitative or quantitative) to the establishment of national
standards and regulations. This approach should lead to standards and
regulations that can be readily implemented and enforced.
The establishment of drinking-water quality standards must
follow a very careful process in which the health risk is considered alongside
other factors, such as technical and economic feasibility. When establishing
national standards, consideration must be given to the practical measures that
will need to be taken with respect to finding new sources of water supply,
instituting certain types of treatment, and providing for adequate surveillance
and enforcement.
National standards will, of necessity be influenced by national
priorities and economic factors such as lack of resources for water treatment or
unavailability of alternative water supply sources. Such economic factors,
conflicting national priorities, and varying local geographical, dietary and
industrial conditions may lead to national standards that differ appreciably
from the WHO Guideline Values (GV). The final judgement as to whether the
benefit from adopting any of WHO recommended GV does or does not justify the
risk is for each country to decide. However, considerations of policy and
convenience must never be allowed to endanger public health.
The Standards Setting Process
Formulation of standards to protect health usually occurs in two
stages, as follows:
(1) The scientific or risk assessment stage
The process for assessment of human health risks associated with
exposure to microbial or chemical contaminants is multifaceted and incorporates
some of all of the following steps:
- Hazard identification -
Utilisation of all available data (epidemiological, animal-bioassay, in
vitro, structure-activity relationship) to determine whether an agent can
cause an adverse effect in humans;
- Dose-response assessment - Determination of the
quantitative relationship between the dose and the incidence of adverse health
effects;
- Exposure assessment - Estimation of the dose, or level
of an agent to which various individuals, or populations are exposed;
- Risk characterisation - Estimation of the incidence and
severity of the adverse effects that are liable to occur in a population due to
actual or predicted exposure.
At the conclusion of this stage it should be
possible to define levels of pollutants that will not result in appreciable
health risk in an exposed population.
(2) The political and administrative stage, or risk
management stage
This second stage is situated in the socio-political and
administrative arena and has to cater for a wide variety of sometimes
conflicting interests. Risk management usually includes:
- Determination of acceptable
risk: to view the problem not as a scientific issue, but rather one of
opinion. The judgement of what is an acceptable risk is a matter in which
society as a whole has a role to play;
- Determination of public to be protected: to consider
not only healthy individuals, but also vulnerable population groups;
- Choice of control technology: to formulate a strategy
and to select appropriate control techniques;
- Legislation/standards: to consider existing national
legal framework and identify necessary legal strategies;
- Economics: to strike a balance between costs and
benefits.
The Guidelines have dealt with the scientific stage in
the hope that such international risk assessment would provide a sound
scientific basis for the further development of national standards.
The risk management stage requires knowledge of the technical,
social, financial, legal, and institutional implications of the standards to be
adopted, and is more appropriately carried out by national or regional
authorities. Those who are involved in setting standards know that at this stage
compromises will be inevitable.
Priorities for setting drinking-water standards
(a) The first priority is to make sure that water is
available to consumers, even if the quality is not entirely satisfactory. If
there is a consideration to discontinue use of a contaminated water supply,
there must be provisions made for instituting an alternative water supply.
(b) The second priority is to control the microbiological
quality of the water supply. The consequences of contamination with pathogenic
bacteria, viruses, protozoa and helminths are such that their control must
always be of paramount importance.
(c) Toxic chemicals in drinking-water must also be controlled if
we are to prevent long-term health effects from exposure to contaminants such as
lead, arsenic or certain organic solvents.
(d) Finally, in assessing the quality of drinking-water, the
consumer relies principally on the sense organs. Colour, taste, odour and
appearance of the water, although not directly related to health, must be
acceptable to the consumer. Some countries have elected to issue
recommendations, rather than standards, for these aesthetic
parameters.
Selection of contaminants for setting standards
There are generally insufficient resources available to deal
with all the contaminants that may occur in drinking-water in a country, and it
will be necessary to establish priorities. Figure 1 depicts a qualitative
prioritisation scheme for setting drinking-water standards. Standards should be
set at first for those contaminants that occur frequently and at significant
concentrations in drinking-water and that have the greatest health impact.
Microbiological contaminants belong to this category.
Figure 1: Priorities for setting
standards
All chemicals are not of equal concern. Six criteria are usually
applied in determining the priority chemical contaminants for which
drinking-water standards should be first established. These are:
- Severity and frequency of observed or suspected
adverse health effects. Of importance are substances that are carcinogenic, and
substances which may cause reproductive and developmental effects.
- Extent of production and use.
- Ubiquity and abundance of the pollutant in water.
- Persistence in water. Contaminants that resist environmental
degradation and accumulate in humans, or in water, deserve attention.
- Exposure from drinking-water relative to other sources such as
air or food can be substantial.
- Population exposed. Attention should be paid to exposure
involving a large proportion of the general population, and to selective
exposures of highly vulnerable groups such as pregnant women, new-born children,
the infirm or the elderly.
Legal framework
The format and structure of standards incorporated in legal
instruments vary from country to country. However, any regulation will generally
contain the following (WHO, 1987):
(a) A statement of the legal instrument, together
with a definition of the applicable terms and concepts, specification of the
responsible authority, and of the areas and substances to which the instrument
will apply.
(b) Mention of applicable documents, such as other standards,
specification and regulations.
(c) A detailed description of the requirements, including limits
on pollutants, applicable tests, mandatory control methods, reporting
requirements, etc. Where the requirements are to be implemented over a period of
time, a timetable will be included.
(d) A specific statement of the monitoring, reporting, and
inspection systems; and
(e) A statement describing applicable penalties for
contraventions.
The authority empowered to enact and enforce regulations varies
from country to country. As regards drinking-water standards, the appropriate
authority may be the Ministry of Health or the Environment.
Compliance with drinking-water quality standards
Once standards are established, it is essential to monitor
drinking-water quality to assess compliance with the specified limits and
regulations.
Both the water and health authorities are involved in
monitoring, the health authority being responsible for ensuring that the legal
requirements are met and compliance with standards is achieved.
Monitoring requirements should be appropriate to the needs of
the country. They should not be too complicated and cumbersome as this may, from
the onset, discourage their implementation.
Both the water and health authorities should have properly
equipped laboratory facilities with trained and properly qualified personnel.
The water authority is often required to provide event reports and periodic
reports of water quality to health authorities, and sometimes to the public.
The water authority, as producer, and the health authority, as
overseer, are both accountable for the quality of water supplies.
Conclusion
In developing national drinking-water standards, it will be
necessary to take account of a variety of geographical, socio-economic, dietary,
and other conditions affecting potential exposure. This may lead to national
standards that differ appreciably from the guideline values.
The number of chemical contaminants for which guideline values
are recommended is very large. It is unlikely that all of these chemical
contaminants will occur in all water supplies or even in all countries. Care
should therefore be taken in selecting substances for which national standards
will be developed.
In developing national standards, care should be taken to ensure
that scarce resources are not unnecessarily diverted to the development of
standards and the monitoring of substances of relatively minor importance.
Priorities must be established, and this should be done in direct relation to
the potential adverse health effects and magnitude of exposure. For instance, in
cases where drinking-water contributes little to the overall exposure, standards
and other risk management strategies should be directed to media (e.g. air,
food) which are important in contributing to total exposure.
The establishment of standards should take into account the
possibilities for implementation in view of the socio-economic constraints
facing a country.
In all countries, including the richest, choices must be made.
The potential consequences of microbial contamination are such that
microbiological standards must take precedence over standards for disinfectants
and their by-products.
References
National Research Council (1983). Risk assessment in the Federal
Government: Managing the process - National Academy Press. Washington, D.C.
World Health Organization (1987). Setting environmental
standards - Guidelines for decision making. Geneva.
Presentation Plan
|
Section |
Key Points |
OHP |
|
Introduction |
· aim of setting national
standards is to protect public health. Standards must be implemented and
enforced through legislative framework |
1 |
|
· the WHO Guidelines are
intended to be used as a basis for establishing national standards |
|
|
· it is not considered
appropriate to set international standards |
|
|
· national standards must
consider national priorities, economic factors, technical feasibility and health
risk. |
|
|
· these will vary between Member
States |
|
|
The standard setting process |
· this is done in two stages:
|
2 |
|
|
1. scientific or risk assessment stage - 4 steps - largely dealt
with by the Guidelines |
|
|
|
2. political and administrative stage - 5 factors to be
considered - to be carried out by national/regional authorities |
|
|
Priorities for setting drinking-water standards |
· there are four priorities for
standards: |
3,4 |
|
|
1. unrestricted availability of water to consumers |
|
|
|
2. control of microbiological quality of water supply |
|
|
|
3. control of toxic chemicals |
|
|
|
4. aesthetic standard of water |
|
|
Selection of contaminants for setting standards |
· resources are the limiting
factor to deal with contaminants, therefore priorities need to be set based on
frequency and concentration of occurrence and health risk. Microbiological
contaminants are a priority |
5 |
|
· six criteria have been
identified to prioritise chemical contaminants. |
|
|
· when setting standards, need
to establish costs of meeting standards, current water quality status and
resources available to meet national standards |
|
|
Legal framework |
· format and structure of
standards in legal instruments vary between countries but generally have 5
common components - |
6 |
|
|
1. statement of the legal instrument |
|
|
|
2. mention of applicable documents |
|
|
|
3. detailed description of the requirements |
|
|
|
4. statement of the monitoring, reporting and inspection systems
|
|
|
|
5. statement of penalties for contraventions |
|
|
Compliance with drinking-water standards |
· to ensure compliance with
standards the quality of the drinking-water must be monitored by the appropriate
bodies |
8 |
|
· monitoring regime must be
appropriate to the country's needs |
|
|
· monitoring requires adequate
equipment and trained personnel |
|
|
Conclusion |
· drinking-water quality
standards may vary nationally due to differing conditions and may be appreciably
different from guideline values |
|
|
· GVs are recommended for a
large number of chemical contaminants and not all are applicable to every
country |
|
|
· countries must prioritise
substances to develop national standards. These should take into account health
risks and magnitude of exposure primarily, as well as resources to ensure
implementation |
|
