Water Safety Plan
Guide
Treatment Processes
– Softening
Version 1, Ref P8.3
January 2014
Citation: Ministry of Health. Water Safety Plan Guide: Treatment
Processes – Softening, Version 1, ref p8.3. Wellington: Ministry of
Health.
Published in January 2014
by the Ministry of Health
PO Box 5013, Wellington, New Zealand
ISBN: 978-0-478-42752-3 (print)
ISBN: 978-0-478-42753-0 (online)
Previously published in 2002 as Public Health Risk Management
Plan Guide: Treatment Processes – Softening, Version 1, ref p8.3.
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
Contents
iii
Introduction
1
Risk Summary
2
Risk Information Table
3
Contingency Plans
4
Water Safety Plan Performance Assessment
5
Ref P8.3
Version 1, January 2014
Water Safety Plan Guide:
Treatment Processes – Softening
iii
Introduction
Softening is used in water treatment to remove calcium and magnesium (hardness). High
concentrations of these ions can cause problems with the use of soaps and detergents, and
cause scale build-up on water heating elements. This Guide is concerned with softening
using ion-exchange resins only.
If an event occurs during the ion-exchange softening process (ie, something goes wrong with
the process), germs may grow in the resin bed and cause sickness.
Softening very hard waters can lead to high concentrations of sodium in the water. While
this may give the water a salty taste, it is unlikely to cause sickness.
Ion-exchange softening can be used before ultra-violet disinfection and membrane treatment
processes to stop scale build-up on the lamps or membranes.
The effectiveness of the softening resins can be reduced if they are clogged by iron,
manganese (see Guide P8.2) or organic matter in the water. Treatment processes to remove
these contaminants from the water before it passes through the softener must therefore be
working properly, and the resin bed must be cleaned and regenerated properly.
Ref P8.3
Version 1, January 2014
Water Safety Plan Guide:
Treatment Processes – Softening
1
Risk Summary
The event creating the greatest risk when ion-exchange softening is carried out is the buildup of germs in the resin bed (see P8.3.1).
The most important preventive measures are:

regularly backflush, regenerate and clean the resin in the softener (see P8.3.1).
(References in parentheses are to the Risk Information Table.)
2
Water Safety Plan Guide:
Treatment Processes – Softening
Ref P8.3
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 important.
Causes
Preventive measures
Checking preventive measures
Corrective action
Signs that action
is needed
What to check
Event: BUILD-UP OF GERMS IN THE RESIN BED
Possible hazards: Germs.
Level of risk: Low1
P8.3.1.1

Organic matter
and microorganisms
trapped in the
resin bed.

1
Regeneration of the
resin at the frequency
recommended by the
manufacturer. This will
also back-flush the bed
and remove organic
material.
Regularly clean
(de-foul) the resin
beads with the
recommended cleaning
agent if iron or
manganese are present
in the water.

Carry out treatment to
remove organic matter
from the water before
the softener.

Disinfect the water
before the softener if
this can be done without
damaging the resin, or
precipitating iron or
manganese which will
foul the resin.

Microbiological
quality.

High counts of
total bacteria.

Regenerate and
back-flush.

Calcium.

Magnesium.
Hardness not
being reduced.



Iron.



Manganese.
Iron and/or
manganese not
being removed.
Clean resin to
remove bead
fouling.
Disinfect the
water after the
softener.

Odour.
The consequences of the event, and therefore the level of risk, will be influenced by how well following
disinfection processes work.
Ref P8.3
Version 1, January 2014
Water Safety Plan Guide:
Treatment Processes – Softening
3
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 – Large numbers of germs released into the treated water.
Indicators:
Required
actions:
Responsibility:
4

Faecal indicator organisms or pathogens are continually detected
in the water leaving the plant.

Widespread sickness in the community linked to the water
supply.

Follow the actions given in Figure 3.2 of the DWSNZ:2000.

Identify the reason for the build-up of germs in the resin bed and
rectify.

Record cause of system failure and steps taken to correct.

Modify your water safety plan if necessary.
Manager designated responsible for the water supply.
Water Safety Plan Guide:
Treatment Processes – Softening
Ref P8.3
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:

Levels of hardness.

Iron and manganese concentrations (these metals in their
soluble forms should also be removed by ion-exchange
softening).
Heterotrophic plate counts (if counts are higher after the
softener than before, this shows that germs are growing in
the exchange resin).

How often:


What to do with the
results:
Responsibility:
Ref P8.3
Version 1, January 2014
Water hardness measurements for the sake of process
control should be undertaken as frequently as considered
necessary by the water supplier.
The frequency at which measurements of heterotrophic
plate counts should be made will depend on the
microbiological quality of the water entering the softener.
The frequency should be higher for poor quality than good
quality waters, and experience will help in determining
how often microbiological testing is necessary.

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 the softening process.
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 softening
process are recognised in the plan.

Manager designated responsible for the water supply.
Water Safety Plan Guide:
Treatment Processes – Softening
5
6
Water Safety Plan Guide:
Treatment Processes – Softening
Ref P8.3
Version 1, January 2014