Water Safety Plan
Guide
Surface Water Abstraction –
Lakes and Reservoirs
Version 1, Ref P1.2
January 2014
Citation: Ministry of Health. 2014. Water Safety Plan Guide: Surface
Water Abstraction – Lakes and Reservoirs, Version 1, ref p1.2.
Wellington: Ministry of Health.
Published in January 2014
by the Ministry of Health
PO Box 5013, Wellington, New Zealand
ISBN: 978-0-478-42706-6 (print)
ISBN: 978-0-478-42707-3 (online)
Previously published in 2001 as Public Health Risk Management
Plan Guide: Surface Water Abstraction – Lakes and Reservoirs,
Version 1, ref p1.2. 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
3
Risk Information Table
4
Contingency Plans
10
Water Safety Plan Performance Assessment
13
Ref P1.2
Version 1, January 2014
Water Safety Plan Guide:
Surface Water Abstraction – Lakes and Reservoirs
iii
Introduction
Source water abstraction is the process of taking water from the source to pipe to the
treatment plant or pre-treatment storage. This Guide is concerned with the abstraction of
water from static surface waters (lakes and reservoirs).
If an event related to abstraction occurs (ie, the quantity or quality of water is affected by the
abstraction process), the following could happen:

If there is not enough source water available to meet demand, sickness can be caused
by poor hygiene and by low pressure letting germs and chemicals get into the
distribution system

If the water quality is so poor that the treatment plant can’t treat it, germs and
disinfection by-products can cause sickness

If there is contamination of the lake or reservoir, germs and chemicals can cause
sickness

If a problem with the intake does not allow enough water to be drawn from the source,
sickness can be caused by poor hygiene and by low pressure letting germs and
chemicals get into the distribution system.
Source water abstraction can present risks to the health and safety of the operators. These
are acknowledged, but are not discussed further as such risks are the subject of health and
safety in employment legislation.
When planning to draw water from a source you need to be aware of the requirements of:

the Resource Management Act

specific requirements of local authorities and regional councils.
Drawing water from the source, and the risks associated with it, cannot be viewed in isolation;
the process influences, and is influenced by, other water supply elements:


Which abstraction method is best for your situation will depend on the availability and
quality of the source water (see Guide S1.1):
–
drawing from a lake or reservoir is helpful if the water flow is low, intermittent,
or unlikely to meet demand under all conditions
–
the use of lakes or reservoirs may make contamination from algal blooms more
likely than use of flowing waters (see Guide P4.1)
–
the development of layers of water near the bottom of lakes or reservoirs that
are short of oxygen (anoxic) will influence the design of the intake (see Guide
P4.2).
Which treatment processes are used to treat the water can be affected by the abstraction
method chosen:
–
clarification/sedimentation may not be required if impoundment can reduce the
turbidity of the raw water, and limit its variability (see P5 series Guides)
–
filtration processes that need relatively good quality feed water can be
considered if the water can be improved by the abstraction method (see P6 series
Guides)
Ref P1.2
Version 1, January 2014
Water Safety Plan Guide:
Surface Water Abstraction – Lakes and Reservoirs
1
–
2
the effectiveness of disinfection is improved if the abstraction method can help
reduce turbidity and colour (see P7 series Guides).
Water Safey Plan Guide:
Surface Water Abstraction – Lakes and Reservoirs
Ref P1.2
Version 1, January 2014
Risk Summary
The events creating the two greatest risks involved in abstracting water from the source are
not being able to draw enough water (see P1.2.1), and drawing water that cannot be properly
treated because the quality is too poor (see P1.2.2).
The most important preventive measures are:

make a plan to control the amounts of water that can be safely drawn from the lake/
reservoir and the levels they are to be drawn from under certain conditions and obtain
the necessary Resource Consents (see P1.2.1.1)

put an alarm on the flow from the intake to warn of an intake failure (see P1.2.1.4–4)

destratify the lake/reservoir to stop lower water levels becoming short of oxygen (see
P1.2.2.2)

use multiple depth intakes to adjust the water quality

apply algicide to the lake/reservoir early enough to stop algal blooms (if this problem
is know to happen) (see P1.2.2.2).
(References in parentheses are to the Risk Information Table.)
Ref P1.2
Version 1, January 2014
Water Safety Plan Guide:
Surface Water Abstraction – Lakes and Reservoirs
3
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
Checking preventive measures
Corrective action
Signs that action
is needed
What to check
Event: NOT ENOUGH SOURCE WATER AVAILABLE FOR ABSTRACTION
Hazards: Germs and chemicals that get into the water because of low system pressure; hazards associated
with poor hygiene.
Level of risk: High

P1.2.1.1
Drought.


P1.2.1.2
Resource
consent
limitations.
4
Start water conservation 
measures as soon as

water shortage
becomes likely.

Plan the development
and use of the water
source, and the need to
identify and develop
new sources, based on
the lake/ reservoir’s
safe yield and drought
probability.
Water demand.

Source usage
rate.
Drop in system
pressure.

Customer
complaints
about low
pressure.
Negotiate new resource 
consents or emergency

provisions.
Water demand.

Source usage
rate.


System
pressure.
System
pressure.

Prepare new
resource
consent
application.

Find new
sources.

Increase
storage
capacity.

Partially close
valves through
the network to
equalise
pressures.
Drop in system
pressure.

Find new
sources.
Customer
complaints
about low
pressure.

Increase
storage
capacity.
Water Safey Plan Guide:
Surface Water Abstraction – Lakes and Reservoirs
Ref P1.2
Version 1, January 2014
Causes
Preventive measures
Checking preventive measures
Corrective action
Signs that action
is needed
What to check
Event: RAW WATER QUALITY TOO POOR TO TREAT
Possible hazards: Germs and chemical determinands particularly disinfection by-products (trihalomethanes,
haloacetic acids, chloral hydrate).
Level of risk: High1
P1.2.2.1

Heavy rain
leading to high
levels of
turbidity and
organic matter
in water
entering the
plant.
Take steps to allow
close down of intake
when necessary:
–
–
–
–
–
P1.2.2.2
establish levels of
raw water quality
that the plant
cannot treat
automatic
measurement of
raw water turbidity
and telemetric
warning
River levels.

Storm warnings. 
use regional council
upstream river
levels as an early
warning system

manage treated
reservoir levels to
maximise period
intake can be shut
down
Non-compliance 
with DWSNZ:
2000,
particularly

turbidity,
particle counts,
and E. coli.

Increased filter
backwash

frequency.
Unable to
achieve
effective
chemical
coagulation.

Inspect catchment for
signs of erosion and
slips that will potentially
be ongoing problems.

Adjust intake or change 
offtake to approximately

2–3 metres below
surface.

Surveillance of water
quality and temperature
as warning of the need
to destratify(see Guide
P4.2) the water body or
apply algicide (see
Guide P4.1) before a
bloom develops.
Review
alternative
source options.
Review pretreatment
options.
Slow the rate of
treatment.
Optimise
application of
coagulant
chemicals and
chlorine.
Difficulty in
achieving free
residual
chlorine in
treated water.
install multi-level
intakes.
Turn off treatment.

Raw water

quality (to
determine when
quality is
approaching the
limits of the
plant’s
treatment

capabilities).


High algal
content.
1


Choose best
abstraction
depth.

Modify intake
system.
Algal content.

As for P1.2.2.1.
Water
temperature.

Taste and
odour problems. 
Colour and
development of
scum in raw
water.

Increased
chlorine
demand.

High algal
counts.
Improve
surveillance
procedure.

Activated
carbon dosing
system
available.

Ensure
adequate
contact time
with chlorine/
ozone to
destroy algal
toxins.

Instigate
destratification if
appropriate.

Carry out
algicide
application, if
appropriate.
Treatment plants are usually designed to be able to treat raw waters with a range of turbidity and colour (see
Guide P11). From time to time the raw water quality may exceed these limits, and the treated water quality may
not meet that required by DWSNZ.
Ref P1.2
Version 1, January 2014
Water Safety Plan Guide:
Surface Water Abstraction – Lakes and Reservoirs
5
Causes
Preventive measures
Checking preventive measures
Corrective action
Signs that action
is needed
What to check
Event: RAW WATER QUALITY TOO POOR TO TREAT cont’d

P1.2.2.3
Seasonal
turnovers
typical of deep
lakes and
reservoirs.
Plan for managing
seasonal turnover of
water typically
November/December
and April/May by:
–
–
–
–
–

P1.2.2.4
Water level too
low so forced to
take poorly
oxygenated
water.

carrying out
destratification of
reservoir (see
Guide P4.2)
–
Temperature at
various depths
(indicating
turnover).

As for P1.2.2.1.

Iron and or
manganese
staining on
washing and/or
sloughing from
distribution
pipes.
Dissolved
oxygen
concentration
with depth.

Increased
chlorine
demand.

As for P1.2.2.1.
slowing treatment
plant rate

Improve
surveillance
procedure to
give better
warning of
stratification.

Use of
additional
treatment
processes (eg,
pre-oxidation,
algicide
application,
activated
carbon).

Review
effectiveness of
procedures.

Review
destratification
system
management.
placing emphasis
on using stored
treated water
determining
whether different
coagulants are
necessary for
changed water
quality
planning
supplementary
treatment eg,
potassium
permanganate
dosing (see Guide
P4.3).
Plan for this problem by: 
–
6

Water level.
changing intake to
lower level earlier
than required to
draw oxygenated
water into lower
depths (precipitation
and settling of iron
and manganese).
carrying out
aeration of reservoir
(see Guide P4.2).
Water Safey Plan Guide:
Surface Water Abstraction – Lakes and Reservoirs
Ref P1.2
Version 1, January 2014
Causes
Preventive measures
Checking preventive measures
Corrective action
Signs that action
is needed
What to check
Event: CONTAMINATION OF THE LAKE OR RESERVOIR
Possible hazards: Germs and chemical determinands appropriate to contamination sources.
Level of risk: Moderate2
P1.2.3.1

Contamination
sources (eg,
stock, septic
tanks, chemical
sources) in the
catchment of

lake/reservoir or
the river
catchment.
P1.2.3.2

Microbiological
quality.

Chemical
determinands
appropriate for
likely
contamination
source.
Ensure that changes in
land use (including
urban developments)
and the potential for
contamination they
create, are well
monitored after
commissioning of the
source.

Restrict activities in the
catchment that may
contaminate the water
(see Guide S1.1).

Gather information
about the hydrology of
the catchment before
undertaking
development.

Zone the area and
restrict access by
signage and physical
barriers.

Physical
inspection.

Microbiological
quality.
Publicise public health
issues in local boating
literature.

Human or boat
contamination
in intake area.

2
Identify potential
sources of
contamination when
abstraction site is being
selected (see Guide
S1.1).
Chemical
determinands
arising from
recreational
activities, if
necessary (eg,
aromatics and
their derivatives
from fuel).

No survey of
potential
sources of
contamination
undertaken.

Add treatment
processes to
remove
identified
contaminants.

No hydrological
information
gathered.


No system for
obtaining
information
about changing
land use in
place.
Instigate system
for gathering
information
about land use
changes.

Review
procedures for
restricting
access, and
change as
necessary.

Review
procedures for
exclusion zone,
and change as
necessary.

High E. coli
counts in raw
water.

High E. coli
counts in raw
water.

Observation of
public use of
zone.
The consequences of the event, and therefore the level of risk, will be influenced by the nature of the
contaminants and whether any treatment processes in use are capable of removing the contaminants.
Ref P1.2
Version 1, January 2014
Water Safety Plan Guide:
Surface Water Abstraction – Lakes and Reservoirs
7
Causes
Preventive measures
Checking preventive measures
Corrective action
Signs that action
is needed
What to check
Event: TOO LITTLE WATER CAN BE DRAWN FROM THE INTAKE TO MEET DEMAND
Possible hazards: Germs and chemicals that get into the water because of low system pressure; hazards
associated with poor hygiene).
Level of risk: High3

P1.2.4.1
Screens
damaged or
clogged.

P1.2.4.2
Particularly for a lake
accessible to the public,
restrict access by
zoning, signage,
physical barriers.

Booms and screens to
trap weed/algae.

Regular preventive
maintenance, as
required by the
conditions, and
manufacturers’
specifications:
lubrication, component
replacement, exercise
valves.

Regular inspections of
intake.

Telemetric alarm for low
flows from intake.

Intake inspections,
regularly and directly
after floods etc., with
follow-up action if
required for existing
protection (eg, fences,
vegetation and soil
instability).
Catastrophic
failure (eg,
flood, slips or
earthquakerelated
damage).
P1.2.4.4

Telemetric alarm for low
flows from intake.

Maintenance according
to manufacturers’
recommendations.
Pump failure
(see also Guide
P10).

3
8

Treatment plant 
flow meters.

Limit nutrient input into
the raw water to reduce
clogging by algae and
weed under low-flow
conditions.

Failure of the
intake structure
due to
mechanical or
structural
failure.
P1.2.4.3
Regular inspection and
cleaning of screens,
intensified during times
of flood.
Standby pump with auto
switch to alternate
pumps.

Operate duty and
standby pumps using
an alternate ‘number of
days cycle’.

Telemetric alarm for low
flows.

Flows (from
intake).


Reduced flow.
Inspection
records.
Failure of
significant
componentry.

Preventive
maintenance
log.
No record of
maintenance
programme.

No water.

Alarm activated.

Flood levels.

No water.

Flows (from
intake).

Reduced flow.

Alarm activated.

No water.

No record of
maintenance
programme.

Alarm activated.
Inspection
records.

Telemetric
records.
Modify intake to
protect against
damage, and
reduce
likelihood of
clogging.

Implement plan
to reduce
nutrient input
into source.

Review
maintenance
and inspection
schedule.

New pumps.
No records of
inspection and
cleaning
programme.



The level of risk will probably increase the lower the flow of the water is.
Water Safey Plan Guide:
Surface Water Abstraction – Lakes and Reservoirs
Ref P1.2
Version 1, January 2014
Causes
Preventive measures
Checking preventive measures
Corrective action
Signs that action
is needed
What to check
Event: TOO LITTLE WATER CAN BE DRAWN FROM THE INTAKE TO MEET DEMAND cont’d
P1.2.4.5

Power failure.
Regular inspection of
cabling, power lines and
connectors.

No water.

Alarm activated.

Stand-by generator.

Battery backed-up
alarms.
P1.2.4.6

Construct a fence
around the intake site.

Vandalism/
sabotage.
Damage to the
intake.

Install intruder alarm.

Evidence of
attempts to gain
access to the
intake.
Ref P1.2
Version 1, January 2014

Consult with
power supply
authority.
Water Safety Plan Guide:
Surface Water Abstraction – Lakes and Reservoirs
9
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 – Water quality too poor to treat
Indicators:
Required actions:
Responsibility:
10

Water too turbid or too coloured to treat.

Turbidity of water leaving plant consistently greater than
0.2 NTU‡ (See DWSNZ:2000).

Consider whether to cease abstraction and switch to an
alternative source of potable water until water of acceptable
quality can again be supplied, or to use storage. (Make sure
that the history of any tanker used to cart water has been
investigated before it is used and that the tanker will not
contaminate the water.)

If inadequately-filtered water has entered the reticulation,
inform the MOH.

Monitor particle counts, turbidity or colour levels until they
reach acceptable limits.

Increase chlorine residual as an interim measure.

Restart plant operation, perhaps at a slower rate.

If very poor raw water quality is likely to be a frequent
problem, consider an alternative source, or changes to
abstraction method or treatment.

Record cause of failure and corrective steps taken.

Plan and develop long term countermeasures if needed.

Modify water safety plan (formerly known as a public
health risk management plan, PHRMP) if necessary.
Manager designated responsible for water supplies.
Water Safey Plan Guide:
Surface Water Abstraction – Lakes and Reservoirs
Ref P1.2
Version 1, January 2014
Event – Not enough water reaching the treatment plant
Indicators:
Required actions:
Responsibility:
Ref P1.2
Version 1, January 2014

Reduced, or no, flow reaching the treatment plant.

Unexpectedly high usage.

Structural failure of intake, or pump failure.

Implement the water supplier’s emergency demand
management strategy.

Consider whether to switch to an alternative source of water
until adequate water of acceptable quality can again be
supplied, or to use storage. (Make sure that the history of
any tanker used to cart water has been investigated before
it is used and that the tanker will not contaminate the
water.)

If inadequately-filtered water has entered the reticulation,
inform MOH of the transgression.

Put conservation measures in place.

Close valves at reservoirs to restrict supply if necessary.

Increase chlorine residual as an interim measure.

If appropriate, identify intake problem and rectify.

When restarting the treatment plant, consider doing this at a
slower rate.

Record cause of failure and corrective steps taken.

If shortages occur frequently because of too little water
available at the source, plan for finding and developing a
new source.

Modify water safety plan if necessary.
Manager designated responsible for water supplies.
Water Safety Plan Guide:
Surface Water Abstraction – Lakes and Reservoirs
11
Event – Contamination enters the lake or reservoir
Indicators:
Required actions:

Complaints of discoloured, tasting or smelling water
coming from taps.

Continued contamination of water supply: E coli detected
or Priority 2 chemical concentrations more than 50% of
MAV.

Reports of illness in parts of the community that may be
linked to water quality.

Close intake.

Notify the MOH, and in consultation warn consumers in the
affected area of alternative water supply measures until
further notice.

Identify the source of the contamination, and determine
whether it is likely to be a transient problem and whether
temporary treatment is available.

If problem is transient:

–
drain and flush the affected part of the distribution
system, considering the need to flush with elevated
chlorine concentrations if the incident may have
involved microbiological contaminants (consultation
with the regional council will probably be required
with regard to disposal of the flushed water)
–
monitor an appropriate determinand in the affected
area to determine the success of the contingency
measures, and notify consumers, when the supply is
safe to use, that they will need to flush their taps until
good quality water can again be drawn.
If problem is likely to be long-lasting or permanent:
–
investigate and develop an alternative supply and/or
treatment
–
Responsibility:
‡
provide another source of potable water until water of
acceptable quality can again be supplied.

Record cause of system failure and steps taken to correct.

Modify water safety plan if necessary.
Manager designated responsible for the water supply.
Nephelometric turbidity units.
12
Water Safey Plan Guide:
Surface Water Abstraction – Lakes and Reservoirs
Ref P1.2
Version 1, January 2014
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:
How often:

Flow records.

Turbidity.

State of intake.

Regular inspection of intake and records (frequency will
be site-dependent and should be based on previous
findings). The inspection should include, but not be
limited to, the following:
–
–
–
What to do with the
results:
Responsibility:
Ref P1.2
Version 1, January 2014
after natural or high-risk events
chemical and microbiological analysis results
inspection reports.

Results need to be recorded to meet legislative
requirements or to allow water safety plan performance
assessment. The WINZ database provides a useful tool
for this purpose.

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 the abstraction of water.

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 abstraction
system are recognised in the plan.
Manager designated responsible for the water supply.
Water Safety Plan Guide:
Surface Water Abstraction – Lakes and Reservoirs
13