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

Ref P8.3 Water Safety Plan Guide: 3 Version 1, January 2014 Treatment Processes – Softening Ref P8.3 Water Safety Plan Guide: 4 Version 1, January 2014 Treatment Processes – Softening 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. Risk Summary

The event creating the greatest risk when ion-exchange softening is carried out is the build- up 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.)

6 Water Safety Plan Guide: Ref P8.3 Treatment Processes – Softening 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

What to check Signs that action is needed

Event: BUILD-UP OF GERMS IN THE RESIN BED Possible hazards: Germs. Level of risk: Low1

P8.3.1.1 Regeneration of the resin at the Microbiological High counts of total Regenerate and back- Organic matter frequency recommended by quality. bacteria. flush. and micro- the manufacturer. This will Calcium. Hardness not being Clean resin to remove also back-flush the bed and organisms Magnesium. reduced. bead fouling. trapped in the remove organic material. Iron. Iron and/or Disinfect the water resin bed. Regularly clean (defoul) the manganese not being after the softener. resin beads with the Manganese. removed. recommended cleaning agent if iron or manganese are present Odour. 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.

1 The consequences of the event, and therefore the level of risk, will be influenced by how well following disinfection processes work.

8 Water Safety Plan Guide: Ref P8.3 Treatment Processes – Softening 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 – Large numbers of germs released into the treated water.

Indicators: Faecal indicator organisms or pathogens are continually detected in the water leaving the plant. Widespread sickness in the community linked to the water supply.

Required Follow the actions given in Figure 3.2 of the DWSNZ:2000. actions: 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.

Responsibility: Manager designated responsible for the water supply. 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 Levels of hardness. observe: 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: 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. What to do with the Record results to meet legislative requirements or to allow water results: 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. Responsibility: Manager designated responsible for the water supply.

10 Water Safety Plan Guide: Ref P8.3 Treatment Processes – Softening Version 1, January 2014