/ Water Safety Plan Guide
Treatment Processes
– Cartridge Filtration
Version 1, Ref P6.3
January 2014

Citation: Ministry of Health. 2014. Water Safety Plan Guide: Treatment Processes – Cartridge Filtration, Version 1, ref p6.3. Wellington: Ministry of Health.

Published in January 2014
by the Ministry of Health
PO Box 5013, Wellington, New Zealand

ISBN: 978-0-478-42734-9 (print)
ISBN: 978-0-478-42735-6 (online)

Previously published in 2001 as Public Health Risk Management Plan Guide: Treatment Processes – Cartridge Filtration, Version 1, ref p6.3. This publication’s title and any reference within the text to ‘public health risk management plan’ were changed in January 2014 to reflect the December 2013 legislation change of the term ‘public health risk management plan’ to ‘water safety plan’. No other changes have been made to this document.

This document is available at:

This work is licensed under the Creative Commons Attribution 4.0 International licence. In essence, you are free to: share ie, copy and redistribute the material in any medium or format; adapt ie, remix, transform and build upon the material. You must give appropriate credit, provide a link to the licence and indicate if changes were made.

Contents

Introduction

Risk Summary

Risk Information Table

Contingency Plans

Water Safety Plan Performance Assessment

Ref P6.3Water Safety Plan Guide: 1

Version 1, January 2014Treatment Processes – Cartridge Filtration

Ref P6.3Water Safety Plan Guide: 1

Version 1, January 2014Treatment Processes – Cartridge Filtration

Introduction

Cartridge filtration can be used to treat drinking-water to:

  • remove particles larger than a specified size (including large germs, particularly Giardia and Cryptosporidium)
  • remove specific types of chemicals, both those that may be of importance to health and those that make the water unpleasant to drink.

This Guide is concerned only with the removal of particles and chemicals that are important to health.

Cartridge filtration can partly disinfect water by physically removing large germs, such as Giardia and Cryptosporidium. It cannot, however, remove small germs unless they are attached to larger particles.

If an event occurs during cartridge filtration (ie, the process doesn’t work properly), the following could happen:

  • If particles larger than 2-3 m are not removed, large germs that also pass through the filter can cause sickness
  • If the filter does not remove chemicals it has been installed to remove, these chemicals can cause sickness
  • If germs grow in the filter, these germs can be released into the water and cause sickness.

Cartridge filtration and the risks associated with it cannot be viewed in isolation. How well the cartridge improves water quality is affected by the quality of the raw water (see the S1 series of Guides) and other treatment process used before the filter (see the P5 and P6 series of Guides). Poor cartridge filter performance can reduce the effectiveness of any following disinfection (see the P7 series of Guides.)

Several factors influence how effective cartridge filtration is:

  • number and type of filters used; suitable filters must be selected to remove the target contaminants, and greater flow is best obtained by running more filters side by side than trying to force water faster through a single filter
  • suitability of the filter housing; use of the incorrect housing for the filter will allow contaminants to get past leaky seals
  • maintenance and backwash procedures; poor care of the filter can result in contaminants passing through it, or clogging it, and the flow being reduced
  • pre-filtration; this removes larger particles before the cartridge filter, so that the cartridge filter will not clog as quickly
  • turbidity of the water being filtered; very turbid (cloudy) water will rapidly clog the filter. In these situations pre-filtration is necessary.

Risk Summary

The event creating the greatest risk with cartridge filtration is not removing particles down to 2–3 m in size (see P6.3.1).

The most important preventive measures are:

  • make sure that the seal is clean and that the filter is seated correctly when replacing the cartridge (see P6.3.1.3)
  • do particle removal tests to make sure the filter is properly seated after changing or adjusting cartridges (see P6.3.1.3).

(References in parentheses are to the Risk Information Table.)

Risk Information Table

Reliable information about water quality is essential for the proper management of a water supply. Knowledgeable and skilled staff are also essential for minimising the public health risks associated with water supplies. Please read the staff training (Guide G1) and the monitoring guides (Guide G2). While we haven’t pointed out every detail of how these documents are linked with the present document, the links are many and are important.

Abbreviations: DWSNZ – Drinking-Water Standards for New Zealand; MAV – Maximum acceptable value – see DWSNZ:2000

Causes / Preventive measures / Checking preventive measures / Corrective action
What to check / Signs that action is needed
Event: FILTER NOT REMOVING PARTICLES DOWN TO 2-3 µm IN SIZE
Possible hazards: Protozoan pathogens (Giardia and Cryptosporidium not removed).
Level of risk: High1
P6.3.1.1
Incorrect type of cartridge filter. /
  • Use filters that are certified, or have been assessed, as being capable of removing particles down to 2–3 m in size. See Footnote 2 of Section 3.2.3.1 ofDWSNZ: 2000.
  • Make sure filter cartridge is compatible with the filter housing and record the type of filter used.
/
  • National or international certificate of filter’s capabilities.2
  • Record of filter types used.
  • Particle counting or microscopic particle analysis test results, or the results of any other test approved by the Ministry of Health.
/
  • Cloudiness in the water following filtration.
  • Filter unable to remove more than 99.9% of particles greater than 2-3 µm in size.
  • Customer complaints.
  • Cases of giardiasis or cryptosporidiosis in the community associated with periods of poor water quality.
  • Wrong filter type used.
/
  • Change to a different type of filter.
  • Keep list of filters that are compatible with the housing in use.

1The consequences of the event, and therefore the level of risk, will be influenced by the quality of the source water and the type and effectiveness of any disinfection after cartridge filtration.

2For example, certification under NSF Standard 53 or AS/NZ 4348:1995.

Causes / Preventive measures / Checking preventive measures / Corrective action
What to check / Signs that action is needed
Event: FILTER NOT REMOVING PARTICLES DOWN TO 2-3 µm IN SIZE cont’d
P6.3.1.2
Damage to the seal (cartridge or filter housing). /
  • Check the condition of the filter housing and the cartridge seal when changing filters.
  • Make sure the person replacing the cartridges knows the correct way to do it.
/
  • Keep record of any damage observed.
  • Filter maintenance log.
  • Particle counting or microscopic particle analysis test results, or the results of any other test approved by the Ministry of Health.
/
  • Cloudiness in the water following filtration.
  • Filter unable to remove more than 99.9% of particles greater than 23µm in size entering it.
  • Customer complaints.
  • Cases of giardiasis or cryptosporidiosis in the community associated with periods of poor water quality.
  • Frequent damage to seal.
/
  • Determine whether it is the cartridge or housing that is damaged, and replace damaged unit.
  • Train staff if necessary.
  • Read filter manufacturer’s instructions.

P6.3.1.3
Cartridge is incorrectly seated. /
  • Make sure the cartridge is fitted the correct way round (some are unidirectional).
  • Make sure base of filter housing is wiped clean before reseating filter cartridge.
  • Make sure cover is replaced properly.
  • Conduct test to check satisfactory particle removal immediately after changing or reseating filter (see Section 11 of DWSNZ: 2000).
/
  • Particle counting or microscopic particle analysis test results, or the results of any other test approved by the Ministry of Health.
/
  • Cloudiness in the water following filtration.
  • Filter unable to remove more than 99.9% of particles greater than 2–3 µm in size entering it.
  • Customer complaints.
  • Cases of giardiasis or cryptosporidiosis in the community associated with periods of poor water quality.
  • Frequent incorrect seating of filter.
/
  • Read filter manufacturer’s instructions.

  • Make sure the person replacing the cartridges knows the correct way to do it.
/
  • Train staff if necessary.

Event: FILTER NOT REMOVING PARTICLES DOWN TO 2-3 µm IN SIZE cont’d
P6.3.1.4
Failure of cartridge. /
  • Carry out regular replacement of filter cartridges, and washing of pre-filters, and maintain records of when this is done and what is done.
  • Make sure new batches of cartridges have certificates showing they meet specifications before buying.
/
  • Flow rates, or pressure drop across the filter. (Sudden changes in flow or pressure drop may indicate a ruptured filter or pre-filter.)
  • Particle counting or microscopic particle analysis test results, or the results of any other test approved by the Ministry of Health.
  • Quality documentation with cartridges.
/
  • Cloudiness in the water following filtration.
  • Filter unable to remove more than 99.9% of particles greater than 2-3 µm in size entering it.
  • Customer complaints.
  • Cases of giardiasis or cryptosporidiosis in the community associated with periods of poor water quality.
  • Records not maintained.
/
  • Wash the filter cartridge and discharge to waste until it can be demonstrated that particle removal is again effective.
  • Obtain another batch of cartridges.
  • Consider changing supplier.

P6.3.1.5
Contamination of filter housing when changing the cartridge. /
  • Make sure filter housing is disinfected during cartridge installation, and flush to waste to remove residual disinfectant.
  • Make sure the person replacing the cartridges knows the correct way to do it to avoid contamination.
/
  • Test the water leaving the filter for signs of the disinfectant.
/
  • Disinfectant concentration has not been reduced to an acceptable level.
  • Customer complaints.
  • Cases of giardiasis or cryptosporidiosis in the community associated with periods of poor water quality.
/
  • Continue flushing until the disinfectant concentration reaches an acceptable level (at least less than 50% of its MAV3).
  • Train staff if necessary.

3The consequences of the event, and therefore the level of risk, will be influenced by the quality of the source water.

Causes / Preventive measures / Checking preventive measures / Corrective action
What to check / Signs that action is needed
Event: FILTER NOT REMOVING PARTICLES DOWN TO 2-3 µm IN SIZE cont’d
P6.3.1.6
Flow too high for cartridge design. /
  • Keep flow rate less than design maximum.
/
  • Flow rate.
  • Particle counting or microscopic particle analysis test results, or the results of any other test approved by the Ministry of Health.
/
  • Cloudiness in the water following filtration.
  • Filter unable to remove more than 99.9% of particles greater than 2-3 µm in size entering it.
  • Customer complaints.
  • Cases of giardiasis or cryptosporidiosis in the community associated with periods of poor water quality.
  • Flow too high.
/
  • Reduce flow to within specifications.

Event: FILTER NOT REMOVING TARGET CHEMICAL CONTAMINANTS
Possible hazards: Health-significant chemical determinands.
Level of risk: Low3
P6.3.2.1
Incorrect type of cartridge filter for the type of chemical to be removed. /
  • Make sure filter cartridge is appropriate for the chemical(s) to be removed.
  • Keep a list of filters suitable for removing the necessary chemical determinands.
/
  • List of chemical determinands the filter is approved to remove (this check need only be carried out once before the filter is first installed).
/
  • Concentration of the target chemical is more than 50% of its MAV.
  • Wrong filter type used.
/
  • Replace cartridge with appropriate type.
  • Start keeping a list of suitable filter types for future reference.

P6.3.2.2
Contaminant breakthrough (caused by rupture or exhaustion). /
  • Carry out regular replacement of filter cartridges.
  • Regular inspection.
  • Follow method recommended by the manufacturer to determine when cartridge can no longer remove the target determinand.
  • Keep flow rate less than design maximum.
/
  • Records of filter maintenance and cartridge replacement.
  • Flow rates, or pressure drop across the filter (sudden changes in flow or pressure drop may indicate a ruptured filter or pre-filter).
  • Monitoring records.
  • Target determinand concentration.
/
  • Cartridges not replaced regularly.
  • Flows too high.
  • Inspection records not signed off.
  • Breakthrough of target determinand.
/
  • Develop schedule of replacing filter cartridges.
  • Put inspection schedule in place.
  • Find out method recommended for assessing when the cartridge capacity is exhausted.
  • Reduce flow to within specifications.

3The consequences of the event, and therefore the level of risk, will be influenced by the quality of the source water.

Causes / Preventive measures / Checking preventive measures / Corrective action
What to check / Signs that action is needed
Event: GROWTH OF GERMS IN THE FILTER
Possible hazards: Germs (released from filter into treated water).
Level of risk: Moderate4
P6.3.3.1
Filter used in the wrong situation or beyond its capacity. /
  • Make sure activated carbon cartridges (including those claiming to stop the growth of bacteria) are not used to treat water that has not been pre-disinfected.
  • Regular replacement of filter cartridges (esp. carbon filters). Record dates of replacement.
  • Carry out disinfection of the water prior to the cartridge filter.
/
  • Record of filter type used.
  • Bacteriological quality of water before and after the filter.
  • Recommended filter lifetime and installation dates of cartridge in use.
/
  • Number of bacteria in the water is greater after the filter than before.
  • Customer complaints and sickness.
  • Replacement schedule not followed.
/
  • Install a more appropriate cartridge type or initiate upstream disinfection.
  • Disinfect water downstream.
  • Develop schedule of replacing filter cartridges and maintain records of this.
  • Initiate upstream disinfection.
  • Disinfect water downstream.

4The consequences of the event, and therefore the level of risk, will be influenced by the type of bacterial growth and the type and effectiveness of any disinfection after cartridge filtration.

Contingency Plans

If an event happens despite preventive and corrective actions you have taken, you may need to consult with the Medical Officer of Health to assess how serious a problem is.

Event – Too many particles larger than 2-3 m in the treated water
Indicators: /
  • Turbidity of filtered water is more than 0.2 NTU.‡
  • Compliance with Section 3.2.3.1 of NZDWS:2000 cannot be demonstrated.
  • Cases of giardiasis and cryptosporidiosis reported in the community associated with periods of poor water quality.

Required actions: /
  • Immediately take the treated water off line. Provide another source of potable water until water of acceptable quality can again be supplied.
  • Follow the actions given in Section 3.4.2.1 of DWSNZ:2000.
  • Record cause of failure and corrective steps taken.
  • Modify water safety plan if necessary.

Responsibility: / Manager designated responsible for the water supply.

‡Nephelometric turbidity units.

Water Safety Plan Performance Assessment

To make sure that your supply’s water safety plan (formerly known as a Public Health Risk Management Plan, PHRMP) is working properly, periodic checks are needed. The overview document outlines what needs to be done. The following table provides the detailed information for checking this particular supply element.

What to measure or observe: /
  • Particle counting.
  • Microscopic particle analysis.
Follow the protocols set out in Section 3 of the DWSNZ:2000.
How often: /
  • For populations more than10,000 periodic filter performance testing and on-line particle counting as defined in Table 3.3 DWSNZ:2000.
  • For populations of 10,000 or less, as for populations of more than 10,000, or alternatively by direct microscopy as per Table 3.3 DWSNZ:2000.

What to do with the results: /
  • Results need to be recorded to meet legislative requirements or to allow water safety plan performance assessment. The WINZ database is good for this.
  • The collected data need to be periodically reviewed to see whether problems with this supply element are developing. This should be done as frequently as the manager responsible considers necessary to minimise risk to public health arising from this supply element.
  • Should this review show any unusual incidents, indicate that proper procedures are not being carried out, highlight poor laboratory results or indicate that poor water quality is reaching customers, then review the procedures for managing cartridge filtration.
  • Evaluate the monitoring results, and any actions taken as the result of having to implement a contingency plan, to see if the water safety plan needs modification – eg, preventive measures are up to date; the contingency plan steps are still adequate; and changes to cartridge filtration are recognised in the plan.

Responsibility: / Manager designated responsible for water quality.

Ref P6.3Water Safety Plan Guide: 1

Version 1, January 2014Treatment Processes – Cartridge Filtration