Water Safety Plan
Guide
Pre-treatment Processes
– Algicide Application
Version 1, Ref P4.1
January 2014
Citation: Ministry of Health. 2014. Water Safety Plan Guide: Pretreatment Processes – Algicide application, Version 1, ref p4.1.
Wellington: Ministry of Health.
Published in January 2014
by the Ministry of Health
PO Box 5013, Wellington, New Zealand
ISBN: 978-0-478-42716-5 (print)
ISBN: 978-0-478-42717-2 (online)
Previously published in 2002 as Public Health Risk Management
Plan Guide: Pre-treatment Processes – Algicide application, Version
1, ref p4.1. 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
6
Water Safety Plan Performance Assessment
8
Ref P4.1
Version 1, January 2014
Water Safety Plan Guide:
Pre-treatment Processes – Algicide Application
iii
Introduction
Algae, or cyanobacteria (blue-green algae), in lakes and storage reservoirs can lead to taste
and odour problems and the appearance of substances that cause sickness (toxins).
Compounds that kill algae (algicides) can be used to control algal, or cyanobacterial, growths.
This Guide is concerned with the use of algicides in the raw water; algae, or cyanobacteria,
in the treatment plant may be controlled through the use of disinfectants.
If an event related to algicide use occurs (ie, the quality of water is affected by the use of an
algicide), the following could happen:

if too much algicide is used, the chemical can cause sickness

if the amount of algae, or cyanobacteria, is too large for the algicide to control, toxins
from the algae, cyanobacteria, can cause sickness

if barley straw is used as an algicide, substances from the barley straw can react with
disinfectants to form by-products that cause sickness.
Applying algicides to source waters 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.
Algae, or cyanobacteria, in the source water can interfere with the operation of the treatment
plant. Good control over their growth reduces the need for pre-oxidation (see Guide P4.3).
It also reduces the amount of disinfectant that will be lost by reaction with the algae or
substances they release into the water (see Guides P7.1, P7.2 and P7.3).
Ref P4.1
Version 1, January 2014
Water Safety Plan Guide:
Pre-treatment Processes – Algicide Application
1
Risk Summary
The event creating the greatest risk involved in algicide application is the population of algae,
or cyanobacteria, being so high that the algicide is unable to reduce their numbers and
harmful amounts of toxins are released into the water when cyanobacteria are killed (see
P4.1.2).
The most important preventive measures are:

reduce the quantities of nutrients entering the source water (see P4.1.2.1)

start dosing the algicide before high populations of algae develop (see P4.1.2.2).
(References in parentheses are to the Risk Information Table.)
2
Water Safety Plan Guide:
Pre-treatment Processes: Algicide Application
Ref P4.1
Version 1, January 2014
Risk Information Table
Reliable information about raw 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: TOO MUCH ALGICIDE ADDED TO THE WATER
Possible hazards: Copper (copper sulphate) and manganese (potassium permanganate) and algal toxins
(released from dead alga cells).
Level of risk: Low
P4.1.1.1

Dose
calculations
incorrect.

P4.1.1.2
Over estimation
of volume of
water body.

Provide staff with
training in the
calculation of
algicide doses.
Use, and record,
independent dose
calculations.

Copper.

Manganese.

Dose
calculations log.

Chorophyll.

Algal cell
counts.
Obtain a reliable

determination of the

volume of the water
body.
Ref P4.1
Version 1, January 2014
Copper.

Dead fish in the
lake or reservoir.

Identify shortcomings in staff
training and
rectify.

Characteristic
colouration of the
water.

Complaints of taste
and staining from
consumers.

Increase the pH
prior to
coagulation to
precipitate
metals.

Frequent
inaccuracies in
dose calculations.

Metal concentration
is more than 50% of
its MAV.

Metal concentration 
is more than 50% of
its MAV.

Dead fish in the
lake or reservoir.
Increase the pH
prior to
coagulation to
precipitate
metals.

Characteristic
colouration of the
water.

Complaints of taste
and staining from
consumers.
Manganese.
Water Safety Plan Guide:
Pre-treatment Processes – Algicide Application
3
Causes
Preventive measures
Checking preventive measures
Corrective action
Signs that action is
needed
What to check
Event: TOO MUCH ALGICIDE ADDED TO THE WATER cont’d

P4.1.1.3
Malfunction of
dosing system.


P4.1.1.4
Copper kept
soluble by
binding with
natural organic
matter (result:
high copper
concentration
passes into
distribution
system).
Routine dosing
system
maintenance.
Replacement of
suspect dosing
system with a
reliable unit.

Copper.

Manganese.

Maintenance
log.
Remove natural

organic matter by
coagulation/floccula
tion, and dissolved
air flotation (see P5
Guide series).
Total organic
carbon (TOC).

Metal concentration
is more than 50% of
its MAV.


Dead fish in the lake 
or reservoir.

Characteristic
colouration of the
water.

Complaints of taste
and staining from
consumers.

Maintenance log
shows frequent
maintenance
needed.

Elevated TOC
concentrations.
Identify cause
of fault and
rectify.
Increase the pH
prior to
coagulation to
precipitate
metals.

Replace
controller with
new unit.

Consider
modification of
treatment
processes.
Event: ALGICIDE DOSING CANNOT REDUCE VERY HIGH ALGAL POPULATION
Possible hazards: Algal toxins (some released from dead alga cells).
Level of risk: Moderate – High1

P4.1.2.1
Algicide dosing
started too late.
1
4
Use experience

from earlier years

to identify when
blooms are likely to
develop and start
algicide dosing in
advance.
Chlorophyll.

Algal cell
counts.
Dead fish in the lake 
or reservoir.

Characteristic
colouration of the
water.

Complaints
consistent with toxin
poisoning.
Consider use of
an appropriate
oxidant later in
treatment to
destroy toxins
(see table in
Guide S1.1 for
guidance on
which oxidants
are appropriate
for various algal
species).
The level of risk is linked to the type of algae present, whether they excrete toxins, the type of toxins excreted,
and other treatment processes in use.
Water Safety Plan Guide:
Pre-treatment Processes: Algicide Application
Ref P4.1
Version 1, January 2014
Causes
Preventive measures
Checking preventive measures
Corrective action
Signs that action
is needed
What to check
Event: ALGICIDE DOSING CANNOT REDUCE VERY HIGH ALGAL POPULATION cont’d
P4.1.2.2

Nutrient levels
allowed to get
too high.

Manage the

catchment, or storage

reservoir, to minimise
quantities of nutrients
entering the source
water (see Guide
S1.1).
Chlorophyll.
Algal cell
counts.
Assess whether
destratification (see
Guide P4.2) is
worsening the
situation by mixing
nutrients from lower
levels of the reservoir.

Dead fish in the
lake or
reservoir.

Review catchment
management
practices.

Characteristic
colouration of
the water.

Re-evaluate the
pros and cons of
destratification.

Complaints
consistent with
toxin poisoning.

To reduce
phosphorus
levels, dose
lake/reservoir with
clays (adsorption)
or lime
(precipitation).
Event: DISINFECTION BY-PRODUCT FORMATION WHEN BARLEY STRAW IS USED AS AN ALGICIDE
Possible hazards: Trihalomethanes, haloacetic acids, chloral hydrate.
Level of risk: Low2
P4.1.3.1
Organic matter
leaching from
the barley
straw.
2

Carry out pilot tests to 
determine whether
the barley straw will
result in elevated
disinfection byproduct formation.
Disinfection byproduct
concentrations.

Disinfection byproduct
concentrations
exceed 50% of
their MAV.

A properly
optimised
coagulation/floccul
ation process may
reduce levels of
organic matter.
While the barley straw may release substances from which disinfection by-products (DBP) may form, there may
also be a decrease in substances released by algae from which DBPs may form.
Ref P4.1
Version 1, January 2014
Water Safety Plan Guide:
Pre-treatment Processes – Algicide Application
5
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 – Lake or reservoir overdosed with algicide
Indicators:
Required actions:

Dead fish in the water body.

Consumer complaints of metallic taste and staining.

Knowledge of spillage of algicide into the water body.

Copper or manganese concentrations very much greater
than their MAVs (see DWSNZ:2000).

Notify the MOH, close down raw water intake, and the
treatment plant (depending on how far through the system
the contamination has carried). If necessary, provide
another source of potable water until water of acceptable
quality can again be supplied.

In conjunction with the MOH, evaluate the risk to health
posed by the metal concentrations that have arisen, or are
likely to arise.

Consider:
–
–
Responsibility:
6
if treatment plant is sufficiently large, use jar tests to
determine the conditions that would have to be
created to allow removal of the metal during
treatment. If this is feasible reopen intake and
attempt treatment, running plant output to waste
adjustment of pH of lake/reservoir to precipitate the
metal.

Warn consumers to flush their taps before resuming the
supply of water.

Record cause of system failure and steps taken to correct.

Modify water safety plan (formerly a public health risk
management plan, PHRMP) if necessary.

Manager designated responsible for the water supply.
Water Safety Plan Guide:
Pre-treatment Processes: Algicide Application
Ref P4.1
Version 1, January 2014
Event – Algal toxin concentrations in the water too high
Indicators:
Required actions:

Dead fish in the water body.

Human sickness consistent with algal toxin poisoning.

Visual evidence of algal mats developing in the lake or
reservoir.

Notify the MOH, close down the supply. Provide another
source of potable water until water of acceptable quality can
again be supplied.

In conjunction with the MOH, evaluate the risk to health
posed by algal toxins that have arisen, or are likely to arise.
This will require knowledge of the algae present, the nature
of toxins released, and their susceptibility to oxidation.

Consider (see Guide S1.1):
–
–
–
Responsibility:
Ref P4.1
Version 1, January 2014
increased oxidant/disinfectant doses to destroy the
toxins passing through the treatment plant
an alternative water source
whether water in post-treatment reservoirs can be
used if adequately dosed with oxidant.

Once corrective measures are in place, monitor algal levels
in the raw water and assess whether toxin concentrations in
the treated water are acceptable before again reticulating the
water.

Flush the distribution system.

Warn consumers to flush their taps before resuming the
supply of water.

Record cause of system failure and steps taken to correct.

Modify water safety plan if necessary.

Manager designated responsible for the water supply.
Water Safety Plan Guide:
Pre-treatment Processes – Algicide Application
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:
How often:

Copper/manganese.

Algal counts in the raw water.

Dose calculation records.

State of aquatic life in the lake/reservoir.

During the period when algae may develop in the source
water, daily checks should be made on:
–
–
–
What to do with the
results:
8
the lake/reservoir to assess the state of aquatic life
algicide dose calculation records
the nature of the algae present in the water to
determine whether they may produce toxins.

Samples for the measurement of the metal concentrations
should be taken from the supply intake every fortnight.

The water safety plan itself should be reviewed every six
months to ensure that it adequately covers all possible
sources of risk. (External audits will be undertaken
annually, internal audits can be undertaken in the
intervening six months.)

Record results 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 algicide dosing.
Water Safety Plan Guide:
Pre-treatment Processes: Algicide Application
Ref P4.1
Version 1, January 2014
Responsibility:
Ref P4.1
Version 1, January 2014

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 algicide dosing system are
recognised in the plan.

Manager designated responsible for the water supply.
Water Safety Plan Guide:
Pre-treatment Processes – Algicide Application
9