Overview of the drinking water standards PDF tủ tài liệu bách khoa

Overview of the Drinking-Water Standards Published in October 2003 by the Ministry of Health PO Box 5013, Wellington, New Zealand ISBN 0-478-25860-7 (Internet) This document is available on the Ministry of Health’s website: http://www.moh.govt.nz Contents List of Tables iv Overview of the Drinking-Water Standards 1.1 Introduction 1.2 Scope of the Standards 1.3 Development of the Standards 1.4 Role of the Standards 1.5 Content of the Standards 1.6 Maximum acceptable values (MAV) 1.7 Components of a drinking-water supply Determination of Compliance 11 14 2.1 Introduction 2.2 Compliance and transgression 2.3 Compliance with the Standards / MAVs Microbiological Compliance 14 15 15 22 3.1 Rationale for microbiologocal MAVs 3.2 Microbiological compliance criteria 3.3 Microbiological monitoring requirements 3.4 Remedial action to be taken when transgression of a microbiological MAV occurs Overview of the Drinking-Water Standards 22 24 58 83 iii List of Tables Table 1.1: Summary of the section numbers of the criteria, requirements for sampling and testing, and remedial actions (some in process of changing) Table 3.1: Log credits and conditions for control of protozoa Table 13.1: C.t values for Cryptosporidium inactivation by chlorine dioxide Table 13.1: C.t values for Cryptosporidium inactivation by ozone a Table 13.2: UV dose requirements for Cryptosporidium and virus inactivation credits Table 3.1: Minimum sampling frequency for E coli in drinking-water leaving a treatment plant for E coli compliance criterion Table 3.2a: Minimum sampling frequency for E coli in a distribution system Table 3.2b: E coli sample distribution Table 3.2c: Minimum sampling frequency for E coli in a bulk distribution zone Table 3.4: Minimum measurement frequency and reporting period for turbidity in water leaving each filter, for protozoa compliance for all treatment plants using any form of filtration Table 3.3: Minimum measurement frequency for protozoa compliance for bag and cartridge filters Table 14.8: References to turbidity requirements in these Standards Note: the protozoa bits need redoing iv Overview of the Drinking-Water Standards 13 35 47 48 50 63 68 70 71 71 72 88 Overview of the Drinking-Water Standards 1.1 Suggested changes Introduction Safe drinking-water, available to everyone, is a fundamental requirement for public health The Drinking-Water Standards for New Zealand 2004 replace the Drinking-Water Standards for New Zealand 2000 with effect from January 2005 They detail how to assess the quality and safety of drinking-water The Standards define drinking-water: that is, water intended to be used for human consumption, food preparation, utensil washing, oral hygiene or personal hygiene The Standards provide criteria applicable to all drinkingwater (except bottled water which must comply with the Food Act 1981) Drinking-Water Standards for New Zealand 2004 (DWSNZ 2004) list the maximum concentrations of chemical, radiological and microbiological contaminants acceptable for public health in drinking-water For community drinking-water supplies, the Standards also specify the sampling protocols that must be observed to demonstrate that the drinking-water complies with the Standards Community drinking-water supplies are water supplies that serve more than 25 people for at least 60 days per year All community drinking-water supplies known to the Ministry of Health are listed in the Register of Community Drinking-Water Supplies in New Zealand Possibly Jan 2005 These definitions may need to be amended as the changes in the Building Act and the Health Act regarding self-supplied community purpose buildings come into effect Because of the wide variety of circumstances relating to individual household drinking-water supplies no general sampling recommendations are made for such supplies If there is any concern about the quality of a household's drinking-water, advice on appropriate sampling programmes can be obtained either from the Environmental Health Officers of the local territorial authority or the Health Protection Officers at the public health service provider Toxic chemical contaminants in drinking-water rarely lead to acute health problems except through massive accidental contamination of a supply Before it presents a health risk the water usually becomes undrinkable due to unacceptable taste, odour or appearance Overview of the Drinking-Water Standards The problems associated with chemical contaminants of drinking-water arise primarily from their ability to cause adverse health effects after prolonged periods of exposure Of particular concern are contaminants which have cumulative toxic properties, such as some heavy metals and substances which are carcinogenic Because chemical contaminants of drinking-water not usually give rise to acute effects they are placed in a lower priority category than microbiological contaminants, the effects of which are potentially acute and widespread The control of risks arising from microbiological contamination is, therefore, given priority over the control of risks from chemical contaminants The Drinking-Water Standards for New Zealand 2004 are intended to: • set out the requirements for compliance with the Standards • facilitate consistency of application throughout New Zealand • protect public health while minimising unnecessary monitoring • be appropriate for large and small publicly and privately owned drinking-water supplies DWSNZ 2004 revise a number of small errors in the 2000 edition, update the analytical methods, and make a number of minor changes to improve the interpretation and robustness of the Standards In addition, DWSNZ 2004 include the following significant changes • The use of UV disinfection for inactivation of bacteria, viruses and protozoa • The sections relating to protozoa criteria have been completely restructured • The use of bags as a sole treatment process for removal of protozoa is no longer considered to be adequate • Issues relating to tankered water supply systems have been incorporated new bullets – old ones gone Tankered supplies to come Overview of the Drinking-Water Standards 1.2 Scope of the Standards DWSNZ 2004 are applicable to water intended for drinking, irrespective of its source, treatment, distribution system, whether it is from a public or private supply or where it is used The exception is bottled water, which is subject to different standards set under the Food Regulations MAF Standard D106.1 (1999) ‘Farm Dairy Water’ also covers water quality Added MAF reference The Standards specify maximum acceptable values (MAVs) for the microbiological, chemical and radiological determinands of public health significance in drinking-water and provide compliance criteria and procedures for verifying that the water supply is not exceeding these values The companion publication, Guidelines for DrinkingWater Quality Management in New Zealand, provides additional information about determinands listed in the Standards, the management of drinking-water quality, the derivation of the concepts used in the Standards and references to the publications on which the Standards are based Aesthetic considerations are not covered by the Standards Guideline values for determinand concentrations that should avoid public complaints are given in Table 14.6 and are discussed in the Guidelines These Standards are for the general protection of public health For people with special medical conditions, or for uses of the water for purposes other than drinking, additional or other water quality criteria may apply such as the special requirements of the Animal Products Act, the Food Act, the Dairy Act, and the Meat Act Water quality standards also appear in MAF Standard D106.1 (1999) ‘Farm Dairy Water’ Overview of the Drinking-Water Standards 1.3 Development of the Standards The Standards were developed by the Ministry of Health with the assistance of an Expert Working Group Extensive use was made of the World Health Organization's Guidelines for Drinking-Water Quality and addenda up to 1998 Reference was also made to the Drinking-Water Standards for New Zealand 1984, 1995 and 2000, and to the Australian Drinking Water Guidelines 1996 1998 still the latest? There is a 2003 edition – but not published yet – Task Force notes available Later version of Australian Guidelines promised in 2003 – still coming The Standards are based on the following principles: The Standards define concentrations of chemicals of health significance which, based on current knowledge, constitute no significant risk to health to a person who consumes litres of the water a day over their lifetime (taken as 70 years) It is usually not possible to define a concentration of contaminant (other than zero) at which there is zero risk because there is always some degree of uncertainty over the magnitude of the risk Refer to the data sheets in the Guidelines for details of each determinand The Standards give top priority to health risks arising from microbiological contaminants Control of microbial contamination is of paramount importance and must not be compromised in an attempt to correct chemical problems, such as disinfection by-product formation The Standards set priorities to ensure that, while public health is protected, scarce resources are not diverted to monitoring substances of relatively minor importance The Standards are set to protect public health and apply to health significant determinands only However, as the public generally assesses the quality of its water supply on aesthetic perceptions, guideline values for aesthetic determinands are also provided Refer to the Guidelines for more details Overview of the Drinking-Water Standards Added the word ‘chemicals’ in line 2, bullet Added reference to data sheets Where feasible, the sampling protocols are designed to give 95 percent confidence that the supply has complied Rewritten with the Standards for at least 95 percent of the time A minimum of 76 samples, none of which transgresses the MAV, is required before the Ministry can be 95 percent confident that the supply complies with the Standards for 95 percent of the time To minimise costs to smaller supplies they are given the benefit of the doubt and it is assumed that if 38 successive samples are taken with no transgressions, then they are complying However, if one transgression occurs the doubt no longer exists and to demonstrate compliance they must take as many samples as are necessary to comply with the 'allowable transgression' tables in Section 7.5.2 of the Guidelines However, for those determinands monitored monthly it will take several years of results before this degree of confidence can be attained Use of the DWSNZ under the HDWAB & BA New section on interpretation needed Overview of the Drinking-Water Standards 1.4 Role of the Standards The Drinking-Water Standards for New Zealand 2004 contribute to the safety and quality of drinking-water by: • defining safety standards for drinking-water • detailing how compliance with these Standards is to be demonstrated • facilitating the development of a consistent approach to the evaluation of the quality of the country's drinking-water supplies Four barriers to disease are available in the provision of safe drinking-water Protection of the quality of the raw water source Removal of chemical and microbiological determinands by physical means Inactivation of pathogenic micro-organisms by disinfection processes Prevention of contamination of treated water whilst it is in the network reticulation The Standards provide performance criteria for the second, third and fourth barriers to infection The first barrier is discussed in the Guidelines Overview of the Drinking-Water Standards If using the UV Intensity Setpoint Approach the transmission or absorbance can be measured manually If 95 percent of weekly samples for a year are not less than 94% transmission (or not exceed an absorbance of 0.027) based on a 10 mm cell, then samples can be tested monthly Secure groundwater: The water shall comply with the specification of secure groundwater (Section 3.2.4) No further monitoring is required to demonstrate compliance with the protozoa criterion gauges for example – some may record, some may be read only? Should supplies without autoclean have to monitor something – what, and how often? Like TH and Fe, or NTU more often – and if so, what trigger points, or what = a transgression? 3.3.2.3 Direct measurement of protozoa Direct measurement of protozoa is not used as a compliance criterion at present Protozoa enumeration and viability tests may be used to confirm suspected presence of protozoa but failure to find protozoa does not demonstrate that drinkingwater is free from protozoa The frequency of testing is at the water supplier's discretion, unless otherwise directed by the Medical Officer of Health 3.3.2.4 Monitoring frequencies for Priority 2c micro-organisms Micro-organisms designated as Priority 2c shall be monitored at a frequency specified by the Medical Officer of Health 3.3.3 Microbiological sampling requirements 3.3.3.1 E coli Procedures for sampling, sample preservation, storage and sample transport shall be agreed beforehand with the Ministry of Health recognised laboratory carrying out the analysis, except where special procedures are authorised for small remote drinking-water supplies or for analyses in the field (see Section 3.3.4) In cases where special procedures are authorised, samples shall be collected aseptically, in sterile bottles, using thiosulphate to dechlorinate the sample if necessary Ideally, testing should commence within six hours of sample collection and it must never be 76 Overview of the Drinking-Water Standards Std Meths says 30 hrs – leave it at 24? USEPA says 24 hr holding time OK six hours of sample collection and it must never be delayed more than 24 hours after collection Samples Changed this to 10° C to align with shall be transferred to the laboratory in a cool, dark Std Meths – and USEPA container If delivery time exceeds one hour, samples shall be maintained at no more than 10° C but shall not be frozen If samples cannot be processed immediately upon arrival in the laboratory they should be stored in a refrigerator 3.3.3.2 Free available chlorine (FAC) and chlorine dioxide Measurement of FAC and the residual chlorine dioxide must be made in the field 3.3.3.3 pH The analysis of pH should be carried out as soon as possible after sampling, with a maximum delay of hours unless there is documented evidence that the pH of the water will not change during the interval between sampling and analysis This latter remark applies particularly to groundwater samples Groundwater remark added 3.3.3.4 Turbidity and particle counting Measurement of turbidity and particle counts preferably should be made on-site using a continuous monitor Otherwise a portable instrument or a laboratory remote from the water treatment plant may be used In the latter case, samples shall be transported to the laboratory as soon as possible, at the latest within 36 hours 3.3.3.5 Ozone The ozone residual in water decays rapidly The halflife ranges from less than minute to more than 20 minutes Ozone contactors are sealed vessels with sample lines that penetrate the walls or roof structure of the contactor The detention times in the sample lines should be as short as possible in order to minimize ozone residual decay in the sample lines Preferably less than 10 percent of the ozone should decay in the sample lines 3.3.3.6 UV The operating UV irradiance level shall be monitored continuously by a certified sensor sited at the point at which the irradiance was measured during the Rewritten New Overview of the Drinking-Water Standards 77 performance validation of the appliance, which shall be at the remotest point in the appliance from the UV source Manual UV absorbance or transmission tests shall be conducted on samples that have not been filtered and not been pH adjusted 3.3 Microbiological analytical requirements Maybe add a brief reference to Direct Integrity Tests (mf)? And maybe a bit about Challenge tests for MF, Bag/Cartridge? Delete particle counting if it doesn’t play a role in DWSNZ 3.3.4.1 Introduction Laboratories recognised by the Ministry of Health shall be used for all analyses carried out for the purpose of assessing compliance with these Standards, except where special procedures are authorised for small, remote drinking-water supplies or for analyses in the field The competence of field analysts shall be verified by an assessor accredited for the purpose The limit of detection, precision and uncertainty of test methods should be included on all analytical reports Refer to Part 1000 of Standard Methods for the specification for IANZ accreditation More detailed information about analytical requirements for E coli, free available chlorine, pH, turbidity and particle size is given in the Guidelines for Drinking-Water Quality Management in New Zealand 3.3.4.2 E.coli For convenience, Presence/Absence tests or other rapid methods for E.coli that are acceptable to the Ministry of Health for the purpose may be used for routine monitoring However, should a positive result be obtained, a second sample must be collected within 12 hours (wherever possible) from the same sample site and E coli enumerated by a laboratory recognised by the Ministry of Health The Ministry of Health maintains a register of laboratories recognised for this purpose (see Section 2.1) The remedial procedures following a transgression are specified in Section 3.4 apply 78 Overview of the Drinking-Water Standards This new paragraph added Will it be called the 2004 edition? 3.3.4.3 Free available chlorine Measurement of FAC must be made in the field or online as soon as the sample has been collected Suitable FAC field methods are DPD tablets or powder in foil Amperometric techniques may also be used All methods should be calibrated against the referee method, APHA 4500 Cl F DPD, ferrous ammonium sulphate titrimetric method, at least once every six months When field tests involve colorimetric interpretation, all persons who have undertaken FAC tests shall undertake the calibration exercise against the referee method The identity of the person performing each field test shall be recorded The analyst making the measurement should be familiar with both the referee and field methods and possible causes of inaccuracy Clarified The reading from a continuously monitoring chlorine or chlorine dioxide analyser shall be calibrated against a grab sample from the water (tested by field method) at least once a week at the point where it is continuously monitored The reading on the continuous monitor at the time of taking the grab sample shall be noted Once every six months the grab sample is to be split and an interlaboratory calibration with a Ministry of Health recognised laboratory carried out, on-site The instrument shall be recalibrated if the output as measured from a grab sample and that logged for compliance purposes varies by more than 0.1 mg/L This reading may be different from the reading observed on the instrument display That means: 0.23 and 0.32 mg/L (varies by 0.09) are OK But 0.23 and 0.34 (varies by 0.11) require action That OK? The precautions specified in the Guidelines should be followed 3.3.4.4 pH The pH electrode should be calibrated before each set of measurements is made, and manufacturer’s instructions should be followed for the storage of the electrode when not in use Calibration solutions used should be prepared by an analytical laboratory using the formulations given in the above instructions, or purchased as a certified solution from a chemical manufacturing company Readings from continuous pH monitors should be Overview of the Drinking-Water Standards 79 calibrated on-site against a calibrated hand-held pH electrode once every four weeks Readings should agree to within 0.10 pH units Some rewritten The pH meter should be calibrated every day/time with pH and (or 10) buffers (most samples will fall in this range) Also, pH buffer should be included once a month to check linearity over a wider range For potable waters, many of which in New Zealand are unbuffered, the time taken for the pH to return from measuring the pH buffer to reading the pH of a water supply sample shall be recorded every four weeks If this has become slow, then the electrode needs attention or is unsuitable Meters being used for potable water require special thin glass electrodes to work properly on unbuffered waters "Robust" electrodes are not suitable 3.3.4.5 Turbidity On-line turbidimeters and particle counters should be installed in such a manner that air entrainment, temperature changes, long sample lines, algal growth, low velocities or changing velocities, are minimised To operate a turbidimeter with confidence at around the 0.10 NTU level requires an instrument with a limit of detection better than 0.02 NTU and requires the use of sophisticated calibration techniques Continuous monitors must be calibrated at least as frequently as recommended by the manufacturer Continuous turbidimeters that not use the nephelometric technique need to be calibrated in NTU units The reading from the turbidimeter shall be calibrated against a grab sample from the water leaving the filter at the time of the turbidimeter reading at least once a week Calibration readings should agree to within 0.05 NTU for test samples with turbidity up to 0.50 NTU, and to within 0.10 NTU for test samples above 0.50 NTU Field and laboratory turbidimeters should be checked against a secondary standard that is traceable to a primary standard at least once every day they are used The test technique shall be checked and calibrated 80 Overview of the Drinking-Water Standards Tolerance added if turbidity should be 5 Preferably continuous Preferably continuous Preferably continuous When collecting E coli sample When collecting E coli sample When collecting E coli sample When collecting E coli sample If FAC substitution for E coli testing 1.0 median, none >5 When measuring FAC, or if relevant, ClO2 When testing for E coli option 1.0 median, none >2 (See comment below) 1.0 median, none >2 (See comment below) 1.0 median, none >2 When collecting E coli sample 5.0 NTU applies Or should this be 2.5 NTU instead of 5, ie – the same as the GV? In which case, does turbidity stop being a GV and become a MAV? Not if we say it is always tested as a ‘micro support test’ 1.2 Assuming we add a turbidity requirement for O3, that means all water leaving a treatment plant will now have a turbidity condition on it For treatments a-d, the turbidity test is to show disinfection is probably OK, or as a protozoa surrogate, ie, part of the relevant criteria For the undisinfected and untreated waters, it’s just a general measure of water quality – ie, a GV that now has to be tested regularly? How can we word/sell that? Water in the distribution system Previously, unless FAC tests were being substituted for E.coli tests, turbidity did not have to be measured, unless related to Guideline Value work, such as complaints In NZDWS 2000 the turbidity was to be not >0.5 NTU (for this one criterion) Now all water in the distribution system is given a condition as part of the criterion 2A/2B And this condition is now the same as appears in the Grading So assuming no deterioration in quality after leaving the treatment plant, all water in the distribution system ideally (ie, GV) should have a turbidity 10,000 have to have continuous FAC, then the turbidity of the water leaving the WTP has to be 1.0? 90 Overview of the Drinking-Water Standards ... Contents List of Tables iv Overview of the Drinking- Water Standards 1.1 Introduction 1.2 Scope of the Standards 1.3 Development of the Standards 1.4 Role of the Standards 1.5 Content of the Standards. .. requirements in these Standards Note: the protozoa bits need redoing iv Overview of the Drinking- Water Standards 13 35 47 48 50 63 68 70 71 71 72 88 Overview of the Drinking- Water Standards 1.1... listed in the Standards, the management of drinking- water quality, the derivation of the concepts used in the Standards and references to the publications on which the Standards are based Aesthetic