Treatment Options for Small Drinking-water Supplies



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Treatment Options for Small Drinking-water Supplies

Resources for Drinking-water Assistance Programme


Published in August 2007 by the
Ministry of Health
PO Box 5013, Wellington, New Zealand

ISBN 978-0-478-19145-5 (print)


ISBN 978-0-478-19146-2 (online)
HP 4413

In December 2013, legislation changed the term ‘public health risk management plan’ to ‘water safety plan’. Any reference within the text to ‘public health risk management plan’ has been changed to reflect the new legislation. No other changes have been made to this document.

This document is available at: www.health.govt.nz



Contents


1 Introduction 4

2 Why Should We Treat Water? 5

2.1 Micro-organisms 6

2.2 Chemical contaminants 6

2.3 Prioritising treatment 6

3 Minimisation, Removal and Inactivation 7

4 What are the Options for Water Sources? 8

5 How Much Water Do We Need? 10

6 What are the Options for Treatment? 12

6.1 Introduction 12

6.2 Pre-treatment 16

6.3 Filtration 20

6.4 Disinfection 26

6.5 Control of aggressive or plumbosolvent water 28

7 General Equipment 30

7.1 Pumps 30

7.2 Pipework and connections 30

8 Places to Get Information 31

9 Conclusions 32

10 Worked Examples 33

10.1 Scenario 1: Shorthop Community Hall 33

10.2 Scenario 2: Smalltown water supply 35

10.3 Scenario 3: Buttercup School 38

10.4 Scenario 4: Slipville 41

10.5 Scenario 5: Greenacres Resort 43

10.6 Scenario 6: Kaupapa Marae 44


List of Tables



Table 1: Water quality required for different household activities 5

Table 2: Characteristics of different water sources 8

Table 3: Treatment needed for various water contaminants 12

Table 4: Sources of further information 31


List of Figures



Figure 1: Water contamination from animals 6

Figure 2: Typical water usage during winter and summer periods 10

Figure 3: Raw water reservoir 17

Figure 4: Pre-settling basin 18

Figure 5: Infiltration gallery 19

Figure 6: Disc filter 19

Figure 7: Infiltration gallery 19

Figure 8: Simple aeration unit 20

Figure 9a: Cartridge filter system 21

Figure 9b: Used cartridge filters 21

Figure 10: Methods of particle removal through rapid sand filters 23

Figure 11: Rapid gravity filter 23

Figure 12: Pressure filter 24

Figure 13: Pressure filter during backwash 25

Figure 14: UV disinfection system 28

Figure 15: Existing water supply system at Shorthop Community Hall 33

Figure 16: Adding another storage tank (Option 1) 34

Figure 17: Using cartridge filters and dosing with calcium hypochlorite (Option 2) 35

Figure 18: Disinfecting with a UV system (Option 3) 35

Figure 19: Existing water system for the Smalltown community 36

Figure 20: Disinfecting with sodium hypochlorite (Option 2) 37

Figure 21: Disinfecting with calcium hypochlorite (Option 3) 37

Figure 22: Using a sodium hypochlorite generator (Option 4) 38

Figure 23: Existing water system at Buttercup School 39

Figure 24: Dosing with sodium hydroxide or soda ash (Option 1) 39

Figure 25: Using dolomite media filters (Option 2) 40

Figure 26: Using aeration (Option 3) 41

Figure 27: Existing water system in Slipville 42

Figure 28: Using coagulant dosing and filtration 42

Figure 29: Existing water system at Greenacres Resort 43

Figure 30: Using a ‘greensand’ pressure filter 43

Figure 31: Existing water system at Kaupapa Marae 44

Figure 32: Using a storage system 44

Figure 33: Using pre-filtration and cartridge filters 45




1 Introduction


This booklet and the accompanying DVD Making it Safe provide information about the supply of safe drinking-water to small water supplies serving fewer than 5000 people. For more information, contact your regional Technical Assistance Programme (TAP) Facilitator or see the draft Guidelines for Drinking-water Quality Management for New Zealand (Ministry of Health 2005), available online at http://www.health.govt.nz/moh/water.
Untreated water can be a major health risk as it can contain harmful chemicals, protozoa, bacteria and viruses. Drinking-water that may contain contaminants should be treated to ensure it is safe. This booklet describes the principles and methods of water treatment for small supplies.
The quality of the water and the need for treatment will depend on the source that is chosen. Water sources can generally be described as groundwater, surface water or rainwater.
Most groundwater is naturally filtered as it passes through layers of the earth into underground reservoirs known as aquifers. Water pumped from wells in these aquifers may not need to be treated at all. Note, however, that springs are often fairly shallow so the Drinking-water Standards consider springs to be surface water.
Surface water, which comes from lakes and rivers, often contains dirt and organic matter (see Figure 1), as well as small amounts of other contaminants. It generally requires treatment to be safe and pleasant to drink.
Rainwater in New Zealand is relatively pure as it falls from the sky but it is often contaminated by micro-organisms as it flows over roofs or when it is kept in storage tanks.

2 Why Should We Treat Water?


The water used by a household is divided among a number of activities, which have different requirements for quality, as summarised in Table 1.
Table 1: Water quality required for different household activities

Type of use

Main requirements

Drinking, cooking, food preparation

Biologically and chemically safe

Bathroom

Biologically safe, chemically safe for skin contact

Laundry, toilet flushing

Should not cause stains or damage clothing

Outdoor (eg, irrigation, car washing)

No special requirements but safe for skin contact

Ideally, all of the water supplied to households in New Zealand should be treated to be biologically and chemically safe. This is because it is costly to provide multiple water supplies of different quality, and minimises the risk of incorrect use.


One of the most effective ways of deciding what treatment is required is to write a water safety plan (formerly known as a Public Health Risk Management Plan, PHRMP). This is a simple way of identifying the public health risks in a water supply. Treatment options that will manage these risks can then be selected.
Water safety plans can be straightforward for small supplies.

1. They outline what could go wrong in the water supply that would lead to contamination of the water; eg, high river levels leading to dirty water in the catchment.

2. They identify what would indicate that something has gone wrong; eg, water becomes turbid (cloudy).

3. They identify and prioritise any improvements that are needed; eg, use of stored water when the river water is dirty.


The Drinking-water Standards for New Zealand provide a yardstick for determining whether water is safe to drink. These standards set out maximum allowable values for things that can contaminate drinking-water and the monitoring that is required to demonstrate that the water is safe to drink. They include a section especially for small supplies serving fewer than 500 people. Drinking-water suppliers should try to comply with the drinking-water standards.
Figure 1: Water contamination from animals






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