Water Safety Plan
Guide
Treatment Processes
– Water Transmission
Version 1, Ref P2
January 2014
Citation: Ministry of Health. 2014. Water Safety Plan Guide:
Treatment Processes – Water Transmission, Version 1, ref p2.
Wellington: Ministry of Health.
Published in January 2014
by the Ministry of Health
PO Box 5013, Wellington, New Zealand
ISBN: 978-0-478-42712-7 (print)
ISBN: 978-0-478-42713-4 (online)
Previously published in 2001 as Public Health Risk Management
Plan Guide: Treatment Processes – Water Transmission, Version 1,
ref p2. This publication’s title and any reference within the text to
‘public health risk management plan’ was 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
7
Water Safety Plan Performance Assessment
8
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Version 1, January 2014
Water Safety Plan Guide:
Treatment Processes – Water Transmission
iii
Introduction
Water is transmitted through a water supply in large diameter pipes (trunk mains). This
Guide is concerned with trunk mains, and also open channels and pressure-break tanks that
may be used in some small supplies.
If an event occurs during water transmission (ie, something goes wrong with the supply
components used to carry water), the following could happen:

If contaminants are able to get into the mains, germs and chemicals may cause sickness

If sediments containing contaminants in the pipes are stirred up, germs and chemicals
may cause sickness when the contaminants are carried into the distribution system

If contaminants are able to get into open channel conduits or break pressure tanks,
germs and chemicals may cause sickness.
Staff health may be at risk from a number of site specific issues when working with trunk
mains. These are acknowledged, but are not discussed further as such risks are the subject
of health and safety in employment legislation.
Trunk mains carry water from the source to treatment, and from the treatment plant through
the distribution system. Risks associated with trunk mains following treatment are discussed
in other Guides concerned with the distribution system (see Guides D1, D2.1, D2.2, D2.3
and P10).
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Water Safety Plan Guide:
Treatment Processes – Water Transmission
1
Risk Summary
The two greatest risks involved in water transmission are no water flow (see P2.4.1) and
contaminating material getting into the mains (see P2.1.1).
The most important preventive measures are:

keeping asset management plants up-to-date so old mains likely to need attention are
identified in good time (see P2.1.1)

controlling pressure fluctuations to minimise stress on the system (see P2.1.1).
(References in parentheses are to this Risk Information Table.)
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Water Safety Plan Guide:
Treatment Processes – Water Transmission
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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
Causes
Preventive measures
Corrective
action
Checking preventive measures
Signs that action
is needed
What to check
Event: CONTAMINATION GETS INTO THE TRUNK MAINS
Hazards: Germs; chemical determinands.
Level of risk: High1
P2.1.1

Mains breaks.


P2.1.2

Inspections.

Pressure.

Unexplained or
regular mains
breaks.
Where possible, six-monthly
physical inspection for
deterioration, and always
inspect after extraordinary
events (floods, slips, etc).
Management of pressure
fluctuations and peak
pressures to minimise
stress on the system
according to system
network plan data.

Protect external surfaces
from the effects of the
climate.

Treat water to reduce its
corrosiveness (see Guide
P8.1).

Check and/or modify air
valves to minimise
entrainment caused by very
low or negative pressures.
Air release
valves entrain
contaminated
water or air.

1
Asset management plan
should identify vulnerable
areas and these should be
prioritised for remedial work
or replacement.
Manage pressure
fluctuations to avoid very
low or negative pressures.

Monitor flows from
treatment plant and
reservoirs (preferably
telemetrically) for early
warning of potential
pressure changes.

Make sure water can drain
away from around the valve.

Pressure.

Unexplained
contamination.

Difficulty in
maintaining
chlorine
residuals.

Damaged or
missing air
valves.

Use the
findings of the
asset plan to
prioritise
mains
replacement,
or reprioritise
work plan.

Consider
duplication of
mains.

Review set
pressures.

Repair air
valves and
associated
damage.
In situations in which contamination enters the mains before treatment, the level of risk should be reduced by
adequate treatment processes.
Ref P2
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Water Safety Plan Guide:
Treatment Processes – Water Transmission
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Causes
Preventive measures
Corrective
action
Checking preventive measures
Signs that action
is needed
What to check
Event: CONTAMINATION GETS INTO THE TRUNK MAINS cont’d

P2.1.3
Leaks.
Management of pressure
fluctuations and peak
pressures to minimise
stress on the system and
eliminate negative pressure
conditions.


Annual leak detection and
repair programme.
P2.1.4

Incidental
damage (eg,
floods, slips,
vehiclerelated
incidents).
Quarterly inspection of

vulnerable zones with
appropriate follow-up during
or after incidents (natural
disasters, vehicle accidents,
etc).

Provide adequate physical
protection for trunk mains.
P2.1.5
Visual
inspection.
Inspection.

Regularity of

observed leaks.

Unexplained
water loss.

Number of
reported and
detected
failures.

Modify leak
detection
programme
and asset
plan.
Determine
viability of
improving
level of
protection.
See Guide D2.3 (D2.3.1.2–D2.3.1.9).
Poor repairs
of breaks,
leaks,
incidental
damage, and
penetration of
trunk mains.
Event: SEDIMENT CONTAINING CONTAMINANTS STIRRED UP
Possible hazards: Germs; iron; manganese; possibly heavy metals; aluminium (from coagulant); organic
particulate matter.
Level of risk: Low
P2.2.1
Sediment or
biofilm
allowed to
develop.
P2.2.2

Intake designed to minimise
introduction of sediment into
the treatment plant.

For distribution trunk mains
see Guide D2.3 (D2.3.2).
See Guide D2.3 (D2.3.2).
See Guide D2.3 (D2.3.2).
Velocity too
high.
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Water Safety Plan Guide:
Treatment Processes – Water Transmission
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Version 1, January 2014
Causes
Preventive measures
Corrective
action
Checking preventive measures
Signs that action
is needed
What to check
Event: CONTAMINATION GETS INTO OPEN CHANNEL CONDUITS AND BREAK-PRESSURE TANKS
Possible hazards: Germs; chemical determinands.
Level of risk: High2
P2.3.1
Stock access
to the channel
and break
tanks.
P2.3.2
Surface runoff and subsurface
leaching of
contaminated
water.
P2.3.3




Ensure break pressure
tanks have a well-fitting lid.
Control land use practices
in vicinity of open channel,
particularly stock and
chemical application
(fertiliser, pesticides).
Evidence of
stock having
gained access
to the channel.

Nutrients
(depending on
the nature of
the fertiliser).

High E. coli
counts.

Elevated
chlorine
demand.

Algae of health
significance
present.

Elevated levels
of nutrients.

Visual evidence
of biological
growths.

Abnormally high 
turbidity of
water reaching

plant.

Flow.
Develop maintenance plan
to remove biological
growths.

Algal toxins (if
algae of
concern are
present).
Fence channel and tanks to
keep stock clear.

Increasing
nutrient levels.
Microbiological
quality.

Elevated
chlorine
demand.


Carry out regular checks of
the state of the channel,
and after heavy rain, and
shore up sides as
necessary.

Microbiological
quality.
Ensure flow paths prevent
regions of slow moving
water.

Abnormally high 
turbidity of
water reaching
plant.

High E. coli

counts.


Control land use practices
in the vicinity to reduce
nutrient input.

Microbiological
quality.
Riparian margin along
channel.
Collapse of
the channel
sides.
2
Turbidity.

Deterioration
of water
quality

caused by
increased
biological

activity in
shallow, warm
open
channels.
P2.3.4
Fence channel and tanks to 
keep stock clear.


Visual
inspection.

Temperature.

Nutrients
(nitrogen and
phosphorus).

Turbidity.

Microbiological
quality.

High E. coli
counts.

Elevated
chlorine
demand.

Evidence of
stock having
gained access
to the channel.
Replace the
open channel
with pipes.
Erect fence.
Provide
suitable lid.

Replace the
open channel
with pipes.

Replace the
open channel
with pipes.

Initiate
checks.
Replace the
open channel
with pipes.
Erect fence.
The level of risk is high for those supplies using open channels and break-pressure tanks between the source
and treatment plant, although treatment, including disinfection, should reduce the level of risk.
Ref P2
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Water Safety Plan Guide:
Treatment Processes – Water Transmission
5
Causes
Preventive measures
Checking preventive measures
What to check
Corrective
action
Signs that action
is needed
Event: NO FLOW THROUGH THE TRUNK MAINS
Possible hazards: Germs and chemicals that get into the water because of low system pressure; hazards
associated with poor hygiene.
Level of risk: High
P2.4.1
See P2.1.1.
Mains breaks.
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Water Safety Plan Guide:
Treatment Processes – Water Transmission
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Version 1, January 2014
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 – High levels of contamination enter a trunk main
Indicators:
Required
actions:
Responsibility:

Unexplained water loss or observed damage.

Observed problems with air valves.

Mains break.

Pressure drops.

Elevated turbidity, microbiological counts or chemical
determinand concentrations.

Incidents of illness suspected of being linked to events
associated with the trunk mains.

Increased chlorine demand.

Take microbiological samples to check compliance with
DWSNZ:2000 Section 3.2.2.2 (water leaving the plant) and
Section 3.2.2.3 (in the distribution system) – microbiological
and chlorine requirements. If results indicate a transgression
follow procedure as set out in Figures 3.2 and 3.3 DWSNZ:2000.

If chemical contamination is suspected, monitor concentrations
of the suspected determinand and follow the requirements of
Section 4.4.1 of DWSNZ:2000.

Determine the reason for water loss and leakage, repair and plan
for long term preventative measures.

Review flushing records and pipework repairs in the area of the
repair to confirm all sections of the pipework would have been
flushed, and flush again.

Monitor chlorine residuals and increase residual to ensure an
FAC residual of more than 0.2 mg/L is achieved throughout the
distribution system.

Confirm that proper work practices for pipe repair were
followed.

Review laboratory results and take further samples.

Record cause of system failure.

Modify water safety plan (formerly known as a public health
risk management plan, PHRMP) if necessary.
Manager designated responsible for the water supply.
Ref P2
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Water Safety Plan Guide:
Treatment Processes – Water Transmission
7
Water Safety Plan Performance
Assessment
To make sure that your supply’s water safety plan 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:

Bacteriological sampling of burst main repairs and mains renewal
projects.

Job sheets to record procedures used, observations made and
problems encountered.

Continuous chlorine residual.

Minimal to nil consumer complaints about discoloration, staining
and taste and odours.

E. coli.

Review of incident log books.
These measurements will also be affected by such things as the
performance of the treatment plant.
How often:
What to do with
the results:
8

Bacteriological sampling for three consecutive days after work is
completed should be carried out and E. coli should not be detected
in any of these samples. If E. coli is detected, advise the MoH and
carry out normal corrective procedures (see Section 3.4.1.2
DWSNZ:2000).

Chlorine residuals should be measured after every event.

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 the review flag 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 contamination of trunk
mains.

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
the mains network are recognised in the plan.
Water Safety Plan Guide:
Treatment Processes – Water Transmission
Ref P2
Version 1, January 2014
Responsibility:
Manager designated responsible for water supply.
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Water Safety Plan Guide:
Treatment Processes – Water Transmission
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