Download Water Safety Plan Guide: Treatment Processes * pH Adjustment

Water Safety Plan
Guide
Treatment Processes
– pH Adjustment
Version 1, Ref P8.1
January 2014
Citation: Ministry of Health. 2014. Water Safety Plan Guide:
Treatment Processes – pH Adjustment, Version 1, ref p8.1.
Wellington: Ministry of Health.
Published in January 2014
by the Ministry of Health
PO Box 5013, Wellington, New Zealand
ISBN: 978-0-478-42748-6 (print)
ISBN: 978-0-478-42749-3 (online)
Previously published in 2001 as Public Health Risk Management
Plan Guide: Treatment Processes – pH Adjustment, Version 1, ref
p8.1. 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
6
Water Safety Plan Performance Assessment
8
Ref P8.1
Version 1, January 2014
Water Safety Plan Guide:
Treatment Processes – pH Adjustment
iii
Introduction
Adjustment of the pH level of drinking-water during treatment may be needed to:

make coagulation more effective (see P5 series of Guides)

make the oxidation of iron and manganese more effective (see Guide P8.2)

make disinfection by chlorine more effective (see Guides P7.1 and P7.3)

reduce its corrosiveness [aggressiveness] before distribution.
This Guide is concerned only with the final adjustment before the water is released to the
distribution system. The information in this Guide will also be helpful in identifying events
and preventive actions needed where pH adjustment is used in other stages of treatment.
Adjustment of pH can be done by:

the addition of acidic solutions or carbon dioxide to the water

the addition of alkaline solutions to the water

placing solid alkaline materials (eg, marble or dolomitic material) in contact with the
water

blowing air into the water, or spraying water into the air (to drive off carbon dioxide).
If an event occurs during pH adjustment (ie, the process doesn’t work properly), the following
could happen:

If the pH level of the water is too high, germs can cause sickness because of poor
disinfection by chlorine.

If the pH level of the water is too low, sickness can come from heavy metals dissolved
from plumbing materials by the corrosive water.

Germs can get into the water during aeration and cause sickness even when the pH
levels are acceptable.
The use of pH-adjusting chemicals can present risks to the health of treatment plant staff.
These are acknowledged, but are not discussed further as such risks are the subject of health
and safety in employment legislation.
Ref P8.1
Version 1, January 2014
Water Safety Plan Guide:
Treatment Processes – pH Adjustment
1
Risk Summary
The event creating the greatest risk involved in controlling the pH level of a water is the pH
level becoming too high (see P8.1.1).
The most important preventive measures are:

regularly check that the pH controller’s sensor is properly calibrated (see P8.1.1.2).

regularly check that the dose rates have been set correctly using a second pH probe,
calibrated according to Section 11.1.3.2 of DWSNZ 2000, to measure the pH (see
P8.1.1.3)

put an alarm on the chemical supply to let you know when the chemical supply is
running low (see P8.1.1.5).
(References in parentheses are to the Risk Information Table.)
2
Water Safety Plan Guide:
Treatment Processes – pH Adjustment
Ref P8.1
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
Corrective action
Signs that action
is needed
What to check
Event: pH LEVEL TOO HIGH (poor disinfection by chlorine)
Possible hazards: Germs (not killed by chlorination); chemical determinands (as impurities in dosing chemicals).
Level of risk: Moderate
P8.1.1.1

Dosing
malfunction.
P8.1.1.2
Power failure.
pH.


Maintenance
log.
pH level more
than 8.5.

Frequent repair
needed.
Replacement of
controller if suspect.


Install an alarm to
indicate when the pH
level has gone outside
the intended range.
Maintenance
log not signed
off.

Problems with
chlorination
effectiveness.
pH.

Calibration
schedule.
pH level more
than 8.5.

Problems with
chlorination
effectiveness.

Regular checks on pH

probe calibration using

calibration buffers and a
low ionic strength
‘natural water’ buffer
check.

Training of staff in pH
probe calibration.

Monitoring of pH using
an independently
calibrated pH probe
(see Guide G2).

pH.


Calibration
schedule.
pH level more
than 8.5.

Problems with
chlorination
effectiveness.
Stand-by generator or
battery bank.


Poor continuity
of power
supply.

Problems with
chlorination
effectiveness.
Dose rate set
incorrectly.
P8.1.1.4


Incorrect
calibration of
controller’s pH
probe.
P8.1.1.3
Routine controller and
dosing pump
maintenance (see
Guide P10).

Ref P8.1
Version 1, January 2014
Electrical
supply.

Identify cause
of fault and
rectify.

Replace
controller.

Re-calibrate pH
probe.

Identify staff
training needs
and provide
training.

Adjust controller
set-point.

Refuel
generator (if
necessary).
Water Safety Plan Guide:
Treatment Processes – pH Adjustment
3
Causes
Preventive measures
Checking preventive measures
Corrective action
Signs that action
is needed
What to check
Event: pH LEVEL TOO HIGH (poor disinfection by chlorine) cont’d

P8.1.1.5
Chemical
supply
exhausted.

P8.1.1.6
Maintain a reserve
chemical supply on site.

Make sure chemicals
supplied are delivered
to the correct bins or
containers. Clearly
label bins; operator on
site when chemicals
delivered.
pH.


Chemical
stocks.
pH level more
than 8.5.

Chemical use
record not
maintained.

Problems with
chlorination
effectiveness.

Order urgent
supply of
chemical.

pH.



Supplier’s
certificate of
analysis.
pH level more
than 8.5.
Label chemical
bins.

Chemical bins
not labelled.


Problems with
chlorination
effectiveness.

Concentrations
of healthsignificant
chemical
determinands
more than 50%
of their MAV.
Require
supplier to
ensure that
operator is
present when
chemicals are
delivered.

Check strength of
solutions supplied, or
purity of chemicals
supplied.
Any health
significant
determinands
suspected as
impurities in
treatment
chemicals.

System of independent
checks on dosing
solution preparation.

Select a pH adjustment
chemical that will
improve the pHbuffering capacity of the
water, if pH stability is
poor.

Use chemical(s)
that will provide
improved
buffering of the
water’s pH.

Check chemicals
supplied for presence of
health-significant
chemical contaminants.

Change
supplier.

Routine maintenance
schedule for pumps.

Identify pump
fault and repair
or replace
pump.

Clear, or
replace,
blocked
chemical feed
lines.

Increase the
concentration of
the dosing
solution.2

Replace unit
with one with an
adequate dose
rate.
Chemical
supply
adequate, but
insufficient
solution/gas
reaching the
dosing point.

Routine maintenance
schedule to ensure
chemical supply lines
are not blocked.
P8.1.1.8

Check product
specifications against
estimated maximum
dose rate.
Chemicals
cannot be
dosed at a high
enough rate.

Record chemical use to
provide a guide to the
length of time the
chemical supply is likely
to last.

Incorrect
chemical used,
chemical of
poor quality, or
dosing solutions
prepared at the
wrong strength.1 
P8.1.1.7
Install an alarm to
indicate when the
dosing solution, or gas
cylinder, is running low.

pH.

Chemical dose
system
maintenance
schedule.

pH.

pH level more
than 8.5.

Problems with
chlorination
effectiveness.

pH level more
than 8.5.

Problems with
chlorination
effectiveness.
1
Use of the incorrect chemical includes selection of a chemical which makes pH control more difficult because it
makes no contribution to carbonate alkalinity.
2
This suggested corrective action should be used with caution, as control will be more difficult, and may have to
be regarded as a temporary measure.
4
Water Safety Plan Guide:
Treatment Processes – pH Adjustment
Ref P8.1
Version 1, January 2014
Causes
Preventive measures
Checking preventive measures
Corrective action
Signs that action
is needed
What to check
Event: pH LEVEL TOO LOW
Possible hazards: Heavy metals (cadmium, chromium, copper, nickel, lead antimony).
Level of risk: Low
P8.1.2.1
The same causes, preventive measures, checks and corrective actions as noted in P8.1.1.1–P8.1.1.8 are
appropriate here. Note, however, that the minimum pH should be no less than 7.0, and that problems with
disinfection efficiency are not linked to low pH levels. Further, there is one additional preventive measure
required when pH adjustment is by contact with calcite or a dolomitic material (eg, Akdolit) – see below P8.1.2.2.
P8.1.2.2

Chemical
supply
exhausted.
Regular checks on solid
material remaining (if
accessible).
Event: GERMS INTRODUCED DURING AERATION
Possible hazards: Germs.
Level of risk: Low–moderate3
P8.1.3.1
Microorganisms
introduced into
the water during
aeration, either
in the airstream
or through
animals
entering the
aerator.
3

Netting placed over
aerator grills to stop
entry of larger animals
(eg, birds, rats, etc).

Microbiological
water quality.

E. coli or
coliforms
detected in a
100 ml sample
following the
aerator.

Disinfection of
the water
following
aeration.
The consequences of the event, and therefore the level of risk, will be influenced by the efficacy of subsequent
disinfection processes.
Ref P8.1
Version 1, January 2014
Water Safety Plan Guide:
Treatment Processes – pH Adjustment
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 – pH level higher than maximum acceptable level
Indicators:
Required
actions:
Responsibility:
6

pH levels are above the maximum level set by the water
supplier. (NB: pH probes (glass electrodes) are required to
make measurements in drinking water. Comparators or
colorimeters are too inaccurate.)

Consumer complaints of ‘soapy’ water, or of chemical burns
from water.

Knowledge of a chemical spillage or overdose that may have led
to a high pH water being produced.

Problems with disinfection efficiency when the pH exceeds the
maximum acceptable level (very caustic water may achieve
disinfection through the pH level alone, but may injure the
consumer).

Notify the MOH and shut down the plant if the pH exceeds 10.
Provide another source of potable water until water of acceptable
quality can again be supplied.

Identify the cause of the problem and rectify.

Bring the pH of the water in the reservoir down to less than 8.5,
or dump it (dropping the pH may be required for this anyway –
check on discharge consent), and 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:
Treatment Processes – pH Adjustment
Ref P8.1
Version 1, January 2014
Event – pH level less than minimum acceptable level
Indicators:
Required
actions:
Responsibility:

pH levels are below the minimum acceptable level set by the
water supplier. (NB: pH probes (glass electrodes) are required
to make measurements in drinking water. Comparators or
colorimeters are too inaccurate.)

Knowledge of a chemical spillage or overdose that may have led
to a low pH water being produced.

Widespread consumer complaints of brown or blue staining on
white bathroom fittings.

Widespread consumer complaints of a strong metallic taste in
the water.

Inform the MOH of the situation and shut down the plant if the
pH drops below 5. Provide another source of potable water until
water of acceptable quality can again be supplied.

Identify the cause of the problem and rectify.

Raise the pH of the water in the reservoir until is more than 7, or
dump it (raising the pH may be required for this anyway – check
on discharge consent), and 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.
Ref P8.1
Version 1, January 2014
Water Safety Plan Guide:
Treatment Processes – pH Adjustment
7
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:

pH level.

E. coli (faecal indicator), or coliforms.

Heavy metal concentrations.
Follow the protocols set out in DWSNZ:2000.
Note that the presence of faecal indicators may be influenced by
factors other than the effect of the pH on the disinfection
process, eg, too little chlorine.
How often:

DWSNZ:2000 Section 3.3.2.1.3 states that the pH should
be monitored continuously for supplies serving more than
10,000 people. For smaller supplies, the pH should be
measured when samples for FAC compliance are taken (or
more frequently if there is concern over the system
ensuring adequate control).
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 pH adjustment.

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 pH-adjustment
process are recognised in the plan.
Responsibility:
8
Manager designated responsible for the water supply.
Water Safety Plan Guide:
Treatment Processes – pH Adjustment
Ref P8.1
Version 1, January 2014