Code of Practice on Piped Drinking Water Sampling and Safety Plans

Code of Practice on Piped Drinking Water Sampling and Safety Plans

Code of Practice on Piped Drinking Water Sampling and Safety Plans
First Edition, January 2008
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Table of Contents
Page No.
Foreword 2
Acknowledgment 3
1.0 Definitions and acronyms 4
2.0 Piped drinking water sampling plans 6
2.1 General 6
2.2 Basic water sampling plan 6
2.3 Comprehensive water sampling plan 6
2.4 Sampling plan for operational monitoring 7
2.5 Sampling frequency and parameters 7
2.6 Sampling locations and points 8
2.7 Test Methods 8
3.0 Piped drinking water safety plans 8
3.1 General 8
3.2 Methodology and key steps 9
3.3 Review of the piped drinking water safety plan 11
3.4 Remedial and improvement measures 11
Appendix A
Parameters for operational monitoring of the quality of piped
drinking water
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Foreword
The quality of drinking water for human consumption is of utmost importance in the
protection of the public health.
Today, Singaporeans enjoy safe piped drinking water.
In order to ensure that such a high standard of the quality of piped drinking water is
maintained, preventive measures such as the preparation and implementation of water
sampling and water safety plans play an important role in the production and supply of
drinking water.
These plans must conform to certain standards and should meet certain requirements so that
there is a consistency in the monitoring, assessment and risk management practices adopted
by the piped drinking water suppliers.
This Code of Practice is prepared based on international guidelines such as those published
by the World Health Organization, and aims to provide guidance to the suppliers of piped
drinking water on the preparation of water sampling and safety plans.
It is issued pursuant to Regulation 4 of the Environmental Public Health (Quality of Piped
Drinking Water) Regulations.
To respond to the changing circumstances and needs, revisions may be made to this Code of
Practice from time to time. National Environment Agency (NEA) will keep the suppliers of
piped drinking water updated so that we can work together in our continuing efforts to ensure
a high standard of public health in Singapore.
Director-General of Public Health
National Environment Agency
Singapore
Code of Practice on Piped Drinking Water Sampling and Safety Plans
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Acknowledgement
The National Environment Agency wishes to thank the following members of the Technical
Committee on National Drinking Water Quality Standards for providing valuable advice on
this Code of Practice.
Local members
Prof. Ong Say Leong (Chairman) National University of Singapore
Prof. Ong Choon Nam (Alternative Chairman) National University of Singapore
Prof. Bloodworth Bosco Chen Health Sciences Authority
Dr. Benjamin Koh Ministry of Health
Mr. Chu Sin-I Agri-Food & Veterinary Authority of
Singapore
A/Prof. Hu Jiangyong National University of Singapore
Prof. Loh Teck Peng Nanyang Technical University
A/Prof. Lye Lin Heng National University of Singapore
Prof. Ooi Giok Ling National Institute of Education
Dr. Pranav S. Joshi (Secretary) National Environment Agency
Ms. Seah Huay Leng Agri-Food and Veterinary Agency of
Singapore
A/Prof. Sim Tiow Suan National University of Singapore
Mr. Tai Ji Choong National Environment Agency
Mr. Tiew King Nyau Public Utilities Board
Overseas members
Prof. Michael Rouse Independent consultant, UK
Dr. Joseph Cotruvo Joseph Cotruvo Associates, USA
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1.0 Definitions and acronyms
For the purpose of this Code of Practice, the following definitions and acronyms shall apply:
Drinking water
Piped water for human consumption but does not include piped
water for human consumption that is supplied solely to the Public
Utilities Board.
Hazard A chemical, physical, radiological or biological/microbial agent
that has the potential to cause harm.
Hazardous event An incident or situation that can lead to the presence of a hazard
(what can happen and how).
NEA National Environment Agency
Parameter A property, characteristic, element, contaminant, substance or
organism.
Risk It is the likelihood of identified hazards causing harm in exposed
populations in a specified time frame, including the magnitude of
that harm and/or the consequences.
Supplier Any person who sells or supplies piped drinking water through a
system of supply that uses a water treatment plant and a
distribution network main connected to the service pipes or
storage tanks in any area or to any premises.
Water treatment plant A plant that produces piped drinking water.
Water safety plan A plan describing the risk assessment and risk management
measures that are or are to be used in order to minimize the
likelihood of any piped drinking water failing to comply with the
water quality standards specified in the Schedule of the
Environmental Public Health (Quality of Piped Drinking Water)
Regulations.
Water sampling plan A plan containing information regarding the sampling and testing
of piped drinking water, including —
(a) the parameters to be tested;
(b) the test methods to be used;
(c) the frequency of the tests;
(d) the sampling locations;
(e) the sampling protocol;
(f) the submission of samples of the piped drinking water to
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an approved testing laboratory for analysis; and
(g) such other information as may be required by the Director-
General.
WHO World Health Organization
WHO Guidelines Guidelines for Drinking-Water Quality, incorporating First
Addendum, Volume 1, Recommendations, Third Edition, issued
by WHO in 2006.
The document is available in the public domain from the WHO’s
website: http://www.who.int/en/
WHO document on Water
Safety Plans
“Water Safety Plans - Managing drinking-water quality from
catchment to consumer”, published by WHO, 2005.
The document is available in the public domain from the WHO’s
website: http://www.who.int/en/
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2.0 Piped drinking water sampling plans
2.1 General
A water sampling plan shall consist of a basic water sampling plan, a comprehensive
water sampling plan and a sampling plan for operational monitoring.
2.2 Basic water sampling plan
(Minimum sample numbers for verification of the microbial quality)
(a) A water supplier shall prepare a basic sampling plan to monitor Escherichia
coli bacteria1 from the designated sampling locations in accordance to the
column “Piped supplies” of the Table 4.5 (namely, “Recommended minimum
sample numbers for faecal indicator testing in distribution systems”) of the
WHO Guidelines.
(b) The number of samples to be collected shall be spread throughout the year, as
much as possible in the sampling plan. Thus if 12 samples are planned per
year, the frequency should ideally be set at 1 sample per month.
2.3 Comprehensive water sampling plan
(a) The comprehensive water sampling plan shall include all the water quality
parameters specified under the Schedule of the Environmental Public Health
(Quality of Piped Drinking Water) Regulations, except those parameters
mentioned in paragraphs 2.2(a) and 2.4 (a) and (b).
(b) Sample(s) shall be collected at each entry point to the distribution system or
from such locations where the drinking water is representative of its source (or
sources if they are combined) after the treatment.
(c) The default frequency of sampling shall be at least once a year.
(d) However, certain parameters or contaminants are unlikely to be present in the
drinking water, or will be present only at concentrations much lower than the
drinking water quality standards prescribed. Hence, the water supplier may
propose sampling frequencies for certain parameters that are lower than the
default frequency (for example once every 3-5 years as suggested in Section
4.3.5 and Table 4.5 of the WHO Guidelines), or may propose not to sample
the drinking water for specific parameters/contaminants that are not of
1 Escherichia coli is considered the most suitable index of faecal contamination. In most
circumstances, populations of thermotolerant coliforms are composed predominantly of Escherichia
coli. As a result, this group is regarded as a less reliable but acceptable index of faecal pollution.
Escherichia coli (or, alternatively, thermotolerant coliforms) is the first organism of choice in
monitoring programmes for verification, including surveillance of drinking water quality. If
necessary, proper confirmatory tests must be carried out.
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concern. In doing so, the water supplier shall take into consideration the
following:
(i) The nature and quality of the source water, and the type of the water
treatment used.
(ii) Test results of three successive years showing that the concentration of
the parameter is significantly lower than the water quality standards
prescribed within the Schedule of the Environmental Public Health
(Quality of Piped Drinking Water) Regulations, and that the quality of
drinking water is unlikely to deteriorate.
(ii) The type of pesticides that are not used for the control of pests in the
raw water catchment areas.
2.4 Sampling plan for operational monitoring
(This would also form part of the water safety plan.)
The water suppliers shall carry out sampling of drinking water for the following
parameters as a part of the operational monitoring:
(a) pH, turbidity and chlorine: These parameters shall be tested from the
designated sampling locations more frequently than the parameter Escherichia
coli bacteria mentioned in paragraph 2.2(a).
(b) Aluminium: Where aluminium-based coagulants are used in the water
treatment plants, the concentration of aluminium shall be tested at least once a
month in the drinking water, and controlled at 0.1 mg/litre or less in large
water treatment facilities that serve 10,000 or more people, and 0.2 mg/litre or
less in small facilities that serve less than 10,000 people.
(c) Additional parameters, which are deemed necessary to monitor as a part of the
operational monitoring, preventive measures, water safety plans, or as a result
of any contamination of raw water or an event which is likely to affect the
quality of drinking water. These parameters, for which the water supplier will
propose the frequency of sampling and the control limits, may include some of
the parameters mentioned within Appendix A of this Code of Practice, and
those prescribed within the Schedule of the Environmental Public Health
(Quality of Piped Drinking Water) Regulations.
2.5 Sampling frequency and parameters
(a) The water supplier may select a frequency of sampling higher than that
mentioned in paragraphs 2.2, 2.3 and 2.4, and may even include parameters
other than those specified in the Schedule of the Environmental Public Health
(Quality of Piped Drinking Water) Regulations, in order to ensure
wholesomeness of the drinking water.
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(b) Examples of situations where a water supplier may select higher frequencies
of sampling in the plan include: Initial monitoring of a new supply system,
epidemiological findings of a waterborne disease, good practices or remedial
actions identified during audits and preparation of water safety plans,
operational failure, or any other unsatisfactory situation.
2.6 Sampling locations and points
(a) Unless otherwise specified, the locations of the sampling points shall be, so far
as practicable, representative of the drinking water supplied by the water
supplier. To achieve this, the water supplier may designate multiple sampling
points with backflow prevention devices as necessary.
(b) Sampling points may include taps or devices connected to the water
distribution network, piping systems in the premises where the drinking water
is supplied, and entry points to the distribution systems and locations where
the drinking water is representative of its source (or sources if they are
combined) after the treatment, as mentioned in paragraph 2.3 (b).
2.7 Test methods
(a) The test methods proposed in the sampling plan by the water supplier shall be
those approved by a national accreditation body or that which is performed in
accordance to the procedure(s) issued or endorsed by any international
organization or a regulatory body in another country as the Director-General
may allow.
(b) The accuracy, precision and limit of detection offered by the test method shall
be adequate for which the measurement is to be made.
3.0 Piped drinking water safety plans
3.1 General
(a) A water safety plan shall consist of:
(i) system assessment to determine whether the system of water
production and supply (including that for any proposed or new system)
can deliver water of a quality that meets the piped drinking water
quality standards;
(ii) identification of control measures and assessment of whether these
control measures are effective, through operational monitoring; and
(iii) management plans including documentation and communication.
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(b) The water safety plans will vary in complexity, as appropriate for the situation,
but their elements shall be based on the multiple-barrier principle, the
principles of hazard analysis and critical control points, and other systematic
management approaches.
3.2 Methodology and key steps
(a) The methodology and the key steps in developing a water safety plan shall be
in accordance to the Chapter 4 (“Water Safety Plans”) of the WHO
Guidelines. (For further guidance, the water suppliers can refer to the WHO
document on Water Safety Plans.)
(b) The key steps that water suppliers should follow are outlined in paragraph (c)
to (j) below.
Water safety team
(c) Assemble a team to prepare the water safety plan.
This team should ideally be multi-disciplinary, consisting of managers,
engineers, water quality controllers and technical staff involved in day-to-day
operations. The team should have the knowledge of the water supply system
from source to the point of water consumption and the types of safety hazards
to be anticipated, and should have the authority to implement the necessary
changes to ensure that safe water is produced and supplied.
System assessment
(d) Document and describe the system
This should cover the whole system from the source to the point of supply, or
from the source to the point of consumption if the systems are owned/operated
by the water supplier, and should include the various types of source water,
pollution sources in the raw water, treatment processes, storage and
distribution infrastructure, and measures for source and resource protection.
These descriptions, which can also take the form of flow diagrams, provide an
overview of the supply and an initial understanding of the processes.
(e) Conduct a hazard assessment and risk characterization to identify and
understand how hazards can enter into the water supply. (Also assess the
existing or proposed system.)
(i) The hazard assessment requires that all potential hazards and
hazardous events that could be associated with the water supply,
including the proposed or new water supply systems, are identified.
Such hazard assessment shall also include review of customer
complaints and past events that had affected, or could possibly have
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affected drinking water quality, or sufficiency of supplies and, where
as a result, there was a risk to the health of the consumer.
(ii) Typical areas that should be taken into consideration, but which will
not be limited to, will be as per Table 4.1 (“Examples of information
useful in assessing a drinking-water system”) of the WHO Guidelines.
(iii) The water supplier shall conduct an annual sanitary inspection of the
raw water/supply either as a part of the hazard assessment or as a part
of the verification practice, using a checklist such as that available
within the Appendix C, “Sanitary Inspection Forms” of the WHO
document on Water Safety Plans.
(iv) Once the potential hazards, their sources and hazardous events are
identified, the risk associated with each hazard or hazardous event
should be described by identifying the likelihood of occurrence (e.g.
almost certain, likely, moderately likely, unlikely and rare) and
severity of consequences if the hazard occurred (e.g. catastrophic,
major, moderate, minor and insignificant). An example is provided in
Table 4.3 of the WHO Guidelines.
(v) By using a scoring matrix outlined in Table 4.2 of the WHO
Guidelines, the risk identified as above should be ranked in order to
establish the most significant hazards and hazardous events.
Control measures and operational monitoring
(f) Identify control measures, and define monitoring of the control measures (i.e.
what limits define acceptable performance and how these are monitored).
(i) The control measures shall apply to the operational monitoring
parameters that can be measured, for which limits – target and action
levels - can be set, and which can be monitored with sufficient
frequency to reveal failures in a timely fashion, and for which
procedures for corrective action can be implemented in response to
deviation from limits.
(ii) One of the control measures shall involve the use of only those water
treatment chemicals for the production of piped drinking water, which
are certified by the manufacturer, supplier, laboratory or a national or
international authority to have conformed to the required purity.
(g) Establish procedures to verify that the water safety plan is working effectively,
and will meet the drinking water quality standards.
The water supplier shall establish procedures and shall carry out final checks
on the overall safety of the piped drinking water supply chain.
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(h) Develop supporting programmes (e.g. training, hygiene practices, standard
operating procedures, upgrade and improvement, research and development,
etc.)
The water supplier shall prepare supporting programmes that are necessary to
ensure drinking water safety although they may not directly affect drinking
water quality.
Management plans
(i) Prepare management procedures (including corrective actions) for normal and
“incident” conditions
Such procedures shall document actions to be taken in response to variations
that occur during the normal operational conditions, and during specific
“incident” situations where a loss of control of the system may occur,
including unforeseen and emergency situations (e.g. when it is necessary to
issue a boil water advisory). The actions should spell out communication and
notification to the National Environment Agency, media and
consumers/public, where applicable.
(j) Establish documentation and communication procedures
Under a water safety plan, these shall include, as practicable, the
documentation, records and communication strategies outlined within Section
4.6 of the WHO Guidelines.
3.3 Review of the piped drinking water safety plan
(a) The review of the water safety plan shall be carried out by the water safety
team at least once a year. During the review, changes in the circumstances
from the period when water safety plan was last prepared and was last
reviewed if applicable, shall be examined.
(b) The water safety plan shall be amended to reflect the relevant changes
concerning paragraph 3.2 (c) to (j).
3.4 Remedial and improvement measures
The drinking water supplier shall carry out the necessary remedial and improvement
measures identified during the preparation and review of the water safety plans in
order to minimize the likelihood of any piped drinking water failing to comply with
the water quality standards specified in the Schedule of the Environmental Public
Health (Quality of Piped Drinking Water) Regulations.
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Appendix A
Parameters for operational monitoring of the quality of piped
drinking water
(The supplier shall review this Appendix during the preparation of the piped water safety plan
and its subsequent reviews, to identify the water quality parameters that should be monitored
as a part of the operational monitoring.)
(a) Residual disinfectant level, colony counts (or heterotrophic plate count), chloride,
hardness, conductivity, total dissolved solids, total organic carbon, sulphate,
cryptosporidium, legionella bacteria, clostridium perfringens, odour, taste and
indicator/other parameters described within the Chapter 10, “Acceptability
aspects” of the WHO Guidelines.
(b) Lead and copper in samples collected from the consumers’ tap, or water
distribution network if the former is not maintained by the water supplier.
(c) Turbidity measured at the water treatment plant through on-line monitoring or
grab sampling to achieve a recommended level of maximum 1.0 (Nephelometric
Turbidity Units (NTU) for the water leaving the treatment plant and 5 NTU for
samples at the consumers’ tap - as one of the measures to minimize the risk of
cryptosporidium and other microbial contaminants in drinking water. Particular
consideration should be given to any abnormal increase in the turbidity levels.
(d) On-line monitoring of conductivity, pH, residual chlorine and such other
parameters that can be measured on-line - at the drinking water treatment plant
and/or in the distribution network system.
(e) Any other contaminant, which is likely to be present in the piped drinking water at
concentrations that may pose risk to the public health.
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