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: www.health.govt.nz
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
1
Risk Summary
2
Risk Information Table
3
Contingency Plans
8
Water Safety Plan Performance Assessment
9
Ref P6.3
Version 1, January 2014
Water Safety Plan Guide:
Treatment Processes – Cartridge Filtration
iii
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.
Ref P6.3
Version 1, January 2014
Water Safety Plan Guide:
Treatment Processes – Cartridge Filtration
1
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.)
2
Water Safety Plan Guide:
Treatment Processes – Cartridge Filtration
Ref P6.3
Version 1, January 2014
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
What to check
Corrective action
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 of DWSNZ:

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

Cloudiness in the
water following
filtration.

Filter unable to
remove more than
99.9% of particles
greater than 2-3
µm in size.
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.

Customer
complaints.
Cases of
giardiasis or
cryptosporidiosis
in the community
associated with
periods of poor
water quality.

Change to a
different type of
filter.

Keep list of
filters that are
compatible with
the housing in
use.
Wrong filter type
used.
1
The 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.
2
For example, certification under NSF Standard 53 or AS/NZ 4348:1995.
Ref P6.3
Version 1, January 2014
Water Safety Plan Guide:
Treatment Processes – Cartridge Filtration
3
Causes
Preventive measures
Checking preventive measures
What to check
Corrective action
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).


P6.3.1.3
Cartridge is
incorrectly
seated.
4
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.
Make sure the
cartridge is fitted the
correct way round
(some are
unidirectional).


Keep record of
any damage
observed.

Cloudiness in the
water following
filtration.
Filter
maintenance
log.

Filter unable to
remove more than
99.9% of particles
greater than
2-3 µm in size

entering it.
Particle
counting or
microscopic
particle analysis 
test results, or
the results of

any other test
approved by the
Ministry of
Health.
Customer
complaints.

Frequent damage
to seal.
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.
Read filter
manufacturer’s
instructions.

Read filter
manufacturer’s
instructions.
Filter unable to
remove more than
99.9% of particles
greater than 2–3
µm in size
entering it.

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
re-seating filter (see
Section 11 of
DWSNZ: 2000).

Cases of
giardiasis or
cryptosporidiosis
in the community
associated with
periods of poor
water quality.

Make sure the person
replacing the
cartridges knows the
correct way to do it.

Frequent incorrect 
seating of filter.
Water Safety Plan Guide:
Treatment Processes – Cartridge Filtration
Train staff if
necessary.

Cases of
giardiasis or
cryptosporidiosis
in the community
associated with
periods of poor
water quality.

Determine
whether it is the
cartridge or
housing that is
damaged, and
replace
damaged unit.
Customer
complaints.
Train staff if
necessary.
Ref P6.3
Version 1, January 2014
Causes
Preventive measures
Checking preventive measures
What to check
Corrective action
Signs that action is
needed
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.



P6.3.1.5

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.
Contamination
of filter housing
when changing
the cartridge.
3

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.
Test the water

leaving the filter
for signs of the
disinfectant.
Disinfectant

concentration has
not been reduced
to an acceptable
level.
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.

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.
Records not
maintained.

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.
The consequences of the event, and therefore the level of risk, will be influenced by the quality of the source
water.
Ref P6.3
Version 1, January 2014
Water Safety Plan Guide:
Treatment Processes – Cartridge Filtration
5
Causes
Preventive measures
Checking preventive measures
What to check
Corrective action
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.

Reduce flow to
within
specifications.

Replace
cartridge with
appropriate
type.

Start keeping a
list of suitable
filter types for
future
reference.

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.
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.
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.
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.

3
6

Keep flow rate less
than design
maximum.


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.
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).
Cartridges not
replaced
regularly.

Monitoring
records.

Target
determinand
concentration.
Wrong filter type
used.
Flows too high.
Inspection
records not
signed off.
Breakthrough of
target
determinand.
The consequences of the event, and therefore the level of risk, will be influenced by the quality of the source
water.
Water Safety Plan Guide:
Treatment Processes – Cartridge Filtration
Ref P6.3
Version 1, January 2014
Causes
Preventive measures
Checking preventive measures
What to check
Corrective action
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.
4
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.
The 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.
Ref P6.3
Version 1, January 2014
Water Safety Plan Guide:
Treatment Processes – Cartridge Filtration
7
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:
Required actions:
Responsibility:
‡
8

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.

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.
Manager designated responsible for the water supply.
Nephelometric turbidity units.
Water Safety Plan Guide:
Treatment Processes – Cartridge Filtration
Ref P6.3
Version 1, January 2014
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:
What to do with the
results:
Responsibility:
Ref P6.3
Version 1, January 2014

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.

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.
Manager designated responsible for water quality.
Water Safety Plan Guide:
Treatment Processes – Cartridge Filtration
9