WHO_TN_05_Emergency_treatment_of_drinking_water_at_the_point_of_use.pdf

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TECHNICAL NOTES ON DRINKING-WATER, SANITATION AND HYGIENE IN EMERGENCIES Updated: July 2013 5.1

TECHNICAL NOTES ON DRINKING-WATER, SANITATION AND HYGIENE IN EMERGENCIES

Emergency treatment of drinking-water

at the point of use

Normally, drinking water supplies need to be treated during

and after an emergency to make them safe and acceptable to

the user. Treatment at the point of use is generally quicker and

less expensive to implement than a centralized system, but it

can be more difficult to manage. Only water used for drinking

and preparing food needs to be treated. Nevertheless, this still

amounts to about five litres per person per day. This technical

note describes some of the most common and simple

treatment options suitable for use during an emergency.

Pre-treatment

There are a wide variety of

technologies for treating water at the

point of use. The methods described

below will remove physical and

microbiological pollution, but not

chemical contamination.

Water treatment can make drinking- water that is unsafe at the source

or drinking-water that becomes

contaminated during handling and

storage safer. There are a number of

different methods and the preferred

method or combination of methods

depends on a number of factors

such as source water quality,

including turbidity or number of

suspended particles in the water,

availability of different methods and

supply chains, user preferences and

cost.

Aeration

Aeration brings water into close

contact with air which increases the

oxygen content of the water.

This will:

• remove volatile substances

such as hydrogen sulphide and

methane which affect taste and

odour;

• reduce the carbon dioxide

content of the water; and

• oxidize dissolved minerals such

as iron and manganese so

that they can be removed by

sedimentation and filtration.

Water can be aerated in a number

of ways. One simple method for

householders is to rapidly shake a

container part-full of water for about

five minutes (Figure 5.1), leave it

standing for a further 30 minutes to

allow any suspended particles to

settle.

Figure 5.1.

Aeration by vigorously shaking water

Storage and settlement

If water is turbid it can be allowed

to ‘stand and settle’ to remove

larger particles. However, even after

settling, water should be treated

with a proven method to ensure it

is safe to drink. Additionally, the

suspended solids and some of the

pathogens will settle to the bottom

of the container, removing further

risk. Storage for two days reduces

contamination further still, and also

reduces the number of organisms

which act as intermediate hosts

for diseases such as Guinea worm

infection (dracunculiasis).

Filtration

A filter removes contamination by

physically blocking particles while

letting the water pass through.

Membrane filters

Membrane filters operate using

similar removal mechanisms as

other filters and can be highly

efficacious in removing even smaller

organisms such as viruses. The

manufacturer’s instructions on use

should be adhered to as often such

filters require regular cleaning.

Sand filters

Household filters may be assembled

inside clay, metal or plastic

containers. The vessels are filled

with layers of sand and gravel and

pipework arranged to force the

water to flow upwards or downwards

through the filter. Figure 5.4 shows a

simple upward rapid flow filter.

Ceramic filters

Water passes slowly through a

ceramic or ‘candle’ filter (Figure

5.3). In this process, suspended

particles are mechanically filtered

from the water. Some filters, for

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5.2 TECHNICAL NOTES ON DRINKING-WATER, SANITATION AND HYGIENE IN EMERGENCIES

Emergency treatment of drinking-water at the point of use

example, are impregnated with silver

which acts as a disinfectant and

kills bacteria, removing the need for

boiling the water after filtration.

Ceramic filters can be manufactured

locally, but are also mass-produced.

They have a long storage life so can

be stored in preparation for future

emergencies.

Cover

Inlet

Outlet

300mm

Water

Coarse

sand

Perforated

metal plate Rocks Drain

stopper

Figure 5.4. A simple upward, rapid flow filter

Figure 5.3. Ceramic or ‘candle’ filters

(a) Manufactured unit (b) Candle with jars

(d) Porous jar

Impurities retained by the surface

of the candle need to be brushed

off under running water at regular

intervals.

Disinfection

Disinfection destroys all harmful

organisms present in the water,

making it safe to drink.

Boiling

Boiling is a very effective method of

disinfecting water, but it is energy

consuming. The water should be

brought to a ‘rolling’ boil. Apart from

the high cost of the energy involved

in boiling, the other disadvantage

is the change in taste of the water.

This can be improved by aeration,

by vigorously shaking the water in a

sealed container after it has cooled.

Chemical disinfection

Many chemicals can disinfect water

but the most commonly-used is

chlorine. With appropriate dosing,

chlorine will kill most viruses and

bacteria, but some species of

protozoa (notably cryptosporidium)

are resistant to chlorine. There are

several different sources of chlorine

for home use; in liquid, powder

and tablet form. They vary in size

and strength (i.e. in how much

chlorine they contain) so different

quantities are required depending

on the formulation. Always follow the

manufacturer’s instructions for use.

To prevent misuse, clear instructions

must be given to all users (see

Figure 5.5).

Chlorine compounds should not

be given out to users outside of

the container they are supplied

in by the manufacturer. People

cannot tell how much of the

product to use or how to use it

simply by looking at it!

Solar disinfection (SODIS)

Ultra-violet rays from the sun will

destroy harmful organisms present

in the water.

Fill transparent one- or two-litre

plastic containers with clear water

and expose them to direct sunlight.

The length of time needed for

inactivation of pathogens will vary

depending on the transparency of

the container, intensity of sunlight,

and clarity of the water. In areas

near the equator, on a sunny day 24

hours is likely sufficient or 48 hours

for a cloudy day. Devices are now

available which can be attached to

the bottles to indicate when sufficient

temperatures have been reached for

inactivation. (Figure 5.6),

Cool the water and shake vigorously

before use.

Combined treatment systems

A few large companies have

developed compounds that both

remove suspended particles and

disinfect the water. One such

compound contains a chemical that

helps suspended particles join to

make larger, heavier ones that will

settle to the bottom of the container.

It also contains chlorine that

disinfects the water after settlement

has occurred.

Training on use of technology

Successful emergency programs

provide and effective treatment

method with which the affected

population is already familiar, and

adequately invest in developing

culturally appropriate materials and

approaches to support correct use of

the selected method(s).

(a) Manufactured unit (b) Candle with jars

(d) Porous jar

(a) Manufactured unit (b) Candle with jars

(d) Porous jar

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TECHNICAL NOTES ON DRINKING-WATER, SANITATION AND HYGIENE IN EMERGENCIES 5.3

Emergency treatment of drinking-water at the point of use

Figure 5.6. Solar disinfection (SODIS) Figure 5.7. Tap fitted to a water bucket

Figure 5.5. How to treat water with chlorine tablets (adapted from IFRC, Geneva) * The required number of chlorine tablets depends on size

of container and % of active chlorine in tablets. Before dosing consult with manufacturer’s instructions.

Looking after clean water

There is no point in treating water

if it becomes contaminated again

afterwards. The storage and use of

treated water is just as important as

the treatment process.

Water storage

Water should be stored in clean,

covered containers and kept in a cool

dark place. Wide-necked containers

such as a bucket fitted with a tight

fitting lid are the best as they are easy

to clean between uses.

Is your water clear?

Wash your hands with

water and soap or ash

Put 1 tablet

in a container

x 1

Close container

wait 30 minutes

Is your water dirty?

Put 2 tablets

in a container

x 2

Close container

wait 30 minutes

Water is now

ready to drink

Filter the water

through cloth

Contamination can also occur as

the water is taken out of the storage

container. Hands and utensils may

come into contact with the water so

it is important to encourage users to

wash their hands with soap before

handling drinking water; and to fit a

tap to the storage container so that

water can be poured directly into a

cup or bowl (Figure 5.7).

Hygiene promotion

The benefit of providing safe

drinking-water will be lost if users

do not know how they will benefit.

Changing unhygienic behaviour is

just as important as the provision

of clean water. Emergencies can

provide a good opportunity to

introduce new hygienic practices.

As users settle into a new

environment, they are more likely

to accept changes to their normal

behaviour. For water supply and

sanitation, the most important

practice to change relates to

handwashing. Don’t assume

everyone knows how to wash their

hands properly. Show them.

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Further information

CEHA (2004) Guide to the promotion of drinking-water

disinfection in emergencies http://www.emro.who.

int/ceha/pdf/DrinkingWater_Disinfection_En.pdf

Centers for Disease Control and Prevention. Fact sheets

on HWTS methods. http://www.cdc.gov/safewater/

household-water.html

IFRC (2008) Household water treatment and safe

storage in emergencies http://www.ifrc.org/

Docs/pubs/disasters/resources/responding- disasters/142100-hwt-en.pdf

Shaw, Rod (ed.) (1999) Running Water: More technical

briefs on health, water and sanitation, ITDG, UK.

Smet, J. & Wijk, C. van (eds) (2002) Small community

water supplies Chapter 19. Disinfection, IRC Technical

Paper 40, IRC: Delft http://www.irc.nl/content/

download/128541/351015/file/TP40_19%20

Disinfection.pdf

SODIS (Undated) How do I use SODIS?

http://www.sodis.ch/Text2002/T-Howdoesitwork.htm

United States Agency for International Development.

Environmental helth topics: Household water treatment.

http://www.ehproject.org/eh/eh_topics.html

WHO/UNICEF International Network on Household Water

Treatment and Safe Storage. http://www.who.int/

household_water/resources/en/

Emergency treatment of drinking-water at the point of use

Prepared for WHO by WEDC. Authors: Sam Kayaga and Bob Reed. Series Editor: Bob Reed.

Editorial contributions, design and illustrations by Rod Shaw

Line illustrations courtesy of WEDC / IFRC. Additional graphics by Ken Chatterton.

Water, Engineering and Development Centre Loughborough University Leicestershire LE11 3TU UK

T: +44 1509 222885 F: +44 1509 211079 E: wedc@lboro.ac.uk W: http://wedc.lboro.ac.uk

5.4

Water, Sanitation,

Hygiene and Health Unit

Avenue Appia 20

1211 Geneva 27

Switzerland

Telephone: + 41 22 791 2111

Telephone (direct): + 41 22 791 3555/3590

Fax (direct): + 41 22 791 4159

URL: www.who.int/water_sanitation_health

this publication. However, the published material is being distributed without warranty of any kind, either expressed or implied. The responsibility for the interpretation and

use of the material lies with the reader. In no event shall the World Health Organization be liable for damages arising from its use.

Box 5.1. Handwashing

Everyone should wash their hands with soap

and water:

1) after defecation;

2) before preparing food;

3) before eating food, breastfeeding or

feeding children; and

4) after cleaning a child’s feces.

1a 1b or

2 3 4 5

6 7 8 9