Safe Storage and Treatment of Household Drinking Water:

Scientific Review of the State-of-the-Art

Mark D. Sobsey

University of North Carolina

Chapel Hill, NC 27599 USA

Mark_Sobsey@unc.edu

Introduction and Background

Water:

• the fundamental nutrient

• essential to life

• a public, social and economic good

• a human right

Water and Sanitation Interventions to Reduce Waterborne, Water-washed and Water-related Diseases

• Sanitation: for feces and other household wastes• Hygiene: handwashing and related personal and

household hygiene• Food sanitation• Childcare sanitation and hygiene• Vector control• Water sanitation

– Quantity– Quality

Water Sanitation to Reduce Household and Community Enteric Disease

• The role of microbiologically safe drinking water in reducing household and community enteric disease has been underestimated, under-appreciated and even ignored in both developed and developing countries

• Health impact (enteric disease reduction) is great:– Developed countries: 15-30% (Payment et al. studies)– Developing countries: 6-90%

Background

• Much of the world’s population lacks access to adequate and safe water supplies

• Waterborne disease and death are a worldwide burden in developed and developing countries

• Microbial agents (pathogens) continue to be a major problem in drinking water supplies of developed and developing countries

Household Water Treatment:The Case and Point

Large fraction of the world’s population is not served by a safe water supply– No access to community or household water

supplies derived from suitable sources• No piped (treated) community supplies• No proper boreholes/wells or springs• Contaminated piped water supplies, urban and

rural– “Improved” supplies often are not microbially

safe; misclassified

Prevailing Water Sources and Conditions of too Many of the World’s People

Inadequate water sources, conveyances and household storage practices

• Water collection in any available vessel from an informal source for household storage/use

• Water collection in any available vessel from a borehole, spring or other ground water source

• Informal/illegal collections from or taps onto piped water supplies or diversions from contaminated surface water sources

• Inadequate storage of initially safe/unsafe water that becomes further contaminated unsafe

Previous Guidelines on Drinking Water Quality

• Did not directly address or have relevance to conditions of many people in the World

• Did not directly address or provide relevant guidance on improving water sources, treatment options, delivery, handling and storage practices

• Presumed norm or goal was access to or development of community water supply: – derived from a suitable source – properly treated – properly conveyed by pipes, drawn from a proper well or

collected in a proper storage system – meets WHO or country guidelines for quality

Collected, Stored Household Water Supplies: Correcting Past Misinformation and Interpretations

• Until now, articulated principles for community water supply were not adequately accepted, endorsed, applied and promoted for collected, stored household water

• Prevailing notion that improving the microbial quality of drinking water will have little/no positive impact on health in the absence of adequate sanitation and hygiene is a myth

• This notion is now disproved and rendered incorrect by numerous recent studies of drinking water microbiology and epidemiology (health impact)

Developments in On-site Storage and Treatment of Household Drinking Water

• Appropriate, affordable, effective and socially acceptable treatment technologies and storage systems of proven effectiveness are now available

• They can dramatically improve and protect microbial quality• They can reduce diarrheal and other waterborne diseases

– Epidemiologically proven by intervention and other types of studies

• Effective even without other hygiene measures, such as improved sanitation

• Such findings are summarized here

Household Water Storage: Disease Risks and Containers for Improved Protection

• Inadequate storage results in microbial contamination and waterborne disease

• Improved storage vessels reduce microbial contamination and disease risks

• Improved storage can be coupled with household treatment to further improve microbial quality and reduce disease risks

• Best implemented and sustained if supported with behavior modification, education, motivation and social marketing

Increased Microbial Contamination (Decreased Microbial Quality) and Infectious Disease Risks from Inadequately Stored Household Water

Location StorageVessel

StorageTimes

MicrobialQualityImpact?

Disease Impact? Reference

RuralBangladesh

Water jars 1-2 days Increased V.cholerae

Incr. (~10Xhigher) cholerarates

Spira et al.,1980

Calcutta,India

Wide-mouth vs.narrow-necked

Notreported

Not measured 4X higher cholerainfections w/wide-mouth

Deb et al.,1982

Khartoum,Sudan

Clay jars("zeers") inhomes, etc.

2 days to1 month

Incr. Fecalindicators w/time, summer,w/ dust events

Not Measured Hammadand Dirar,1982

RuralMalawi

Stored HHwater;others

Notreported

Higher fecalcoliforms

Not measured LindskogandLindskog,1988

SouthSudan

Notreported

Notreported

Increased fecalbacteria levels

Not Measured Mascher etal., 1988

Rangoon,Burma

Buckets Up to 2days

Higher FC thansource

Not Measured Han et al.,1989

Increased Microbial Contamination (Decreased Microbial Quality) and Infectious Disease Risks from Inadequately Stored Household WaterLocation Storage

VesselStorageTimes

MicrobialQualityImpact?

Disease Impact? Reference

Urban slumand ruralvillages,Liberia

Largecontainers,open orclosed

"A longtime"

Higher entero-bacters instored thansource water

Not Measured Molbak etal., 1989

Kurunegala,Sri Lanka

Earthenpots andothers

Notreported

Higher FC instoredunboiled water

Not Measured Mertens etal., 1990

Rural Africa Traditional& metal jars

24 hoursor more

Higher TC andFC

Not Measured Empereur etal., 1992

RuralMalaysia

Variouscontainers

Notreported

Higher FC inunboiled thanboiled water

Higher diarrhearisks stored inwide-necked thannarrow-necked

Knight et al.,1992

Trujillo,Peru

Wide-mouthcontainers

Notreported

Higher FC instored thansource waters

Increased cholerarisks

Swerdlow etal., 1992

Characteristics of Preferred Water Storage Vessels• Appropriate material, size, shape, dimensions,

– Depends on collection, Rx method, use conditions & user• Volume: usually 10 and 30 liters (not too heavy)

– smaller volumes (1-1.5 L) for solar Rx; multiples• Handles to facilitate lifting and carrying• Stable base to prevent overturning• Uniform size for standard chemical dosing• Opening: large enough to fill and clean; small enough to

discourage hands, cups or other dip utensils. – Inlet: fitted with a lid

• Durable spigot or spout for pouring

Household Water Containers for Safe Storage:• Material: Depends on Rx; easy to clean; lightweight,

durable, impact- and oxidation- resistant, heat-resistant (if thermal Rx)– High-density polyethylene (HDPE)

for chemical Rx– Transparent beverage bottles

for solar-UV + heat (PET)– Black or opaque for solar-heat only

• Can adapt traditional vessels to safer storage– Add cover– Add spout or spigot

Household Water Containers for Safe Storage

Properties CDC Vessel Jerry Can OxfamComposition Plastic

(HDPE)Plastic Plastic

Volume (L) 20 Varies 14Durability Good Acceptable Good

Cleaning Ease Yes Yes, qualified YesLid Yes Yes Yes

Faucet Yes No YesInside Cleaning Yes No, usually Yes

Chemical Dosing Ease Very easy Easy (may be variable) Very easyCost Med.-High Low Med.-High

Distribution Cost High Low, if local High

Household Treatment: Barrier(s) against Microbial Contamination and Waterborne Disease

Barriers:• Collect from a safe source• Store in a container with contamination

safeguards• Treat to reduce microbial contamination

– Physical treatments– Chemical treatments– Combined physical-chemical treatments

Criteria for Preferred Household Water Treatment Technologies

• Appreciably improves microbial quality– Reduces pathogens

• Reduces waterborne disease risks• Simple to learn, teach and use (low technical difficulty)• Accessible or available

– materials and other requirements• Robust and reproducible• Affordable• Socially and culturally acceptable• Sustainable and spreadable

Physical Methods for Household Water Treatment

Method Availability andPracticality

TechnicalDifficulty

Costa MicrobialEfficacyb

Boiling or heatingwith fuels

Variesc Low-Moderate

Variesc High

Exposure to Sunlight High Low-Moderate

Low Moderate

UV Irradiation(lamps)

Variesd Low-moderate

Moderate-highd

High

Plain Sedimentation High Low Low LowFiltratione Variese Low-

ModerateVariese Variesf

Aeration Moderate Low Low Lowg

A in US dollars/yr: <$10 for low, >$10-100 for moderate and >$100 for high. B <1 log10 (<90%) = low, 1 to 2 log10 (90-99%) = moderate and >2 log10 (>99% = high).cDepends on heating method and availability and fuel costs (range from low-high).dAvailability of & type of lamps, housings, availability & cost of electricity, O&M needs eDifferent ones; practicality, availability, cost and microbial efficacy vary among themg Possible synergism with other Rx (solar disinfection with sunlight)

Boiling (Heating) with FuelAdvantages:• Widely practiced• Effectively inactivates

microbes• Easy to use• Cultural and social

acceptance is widespread

Disadvantages:• Fuel requirement:

– Expensive– Ecological impacts– Small treatable volumes

• No residual for protection from recontamination

• Transfer for storage in another vessel poses recontamination risks

Boiling is not a highly recommended or preferred treatment, despite its widespread use, except where renewable fuel is readily available at low cost

Disinfection by UV Irradiation with LampsAdvantages:• Simple installation

– Esp. units with lamps above shallow water layer

• Microbial efficacy• Flexible operation

Disadvantages:• No residual disinfectant• Recontamination

vulnerability of treated, stored water

• Requires electricity• Requires trained M&O

– Process verification issues• Relatively costly

– initial unit cost– replacement lamp cost and

availability

UV lamp technology is recommended but not highly for use in household water treatment

Recommended Technologies for Physical Treatment

• Solar disinfection with UV + heat: – SODIS and SOLAIR (clear bottle;

black side)– Microbial and epidemiological

data• Solar disinfection with heat:

– black or opaque bottle or pot– solar cooker– solar reflector– Wax temperature indicator– Microbial data

SODIS

clear plastic bottle

Black surface: on bottle or on resting surface

SODIS and SOLAIRAdvantages:• Inactivates pathogens• Disinfects small quantities

of water for consumption • Relies on solar energy only • Does not directly change

chemical quality of water• Apparent synergistic effects

of thermal and UV inactivation mechanisms

• Treatment option for use mainly at household level

Limitations:• Not useful to treat large

volumes of water• Requires relatively clear

water (turbidity <30 NTU) • Needs solar radiation • Exposure times:

– 6 hours under bright sky or up to 50% cloudy sky

– 2 consecutive days under 100% cloudy sky

• No disinfectant residual

Epidemiological Evidence for Diarrheal Disease Reduction by SODIS Solar Disinfection of Household Water

Location % Reduction in Disease

Significant Microbial

Reduction?

Reference

Kenya 86% cholera

Not Reported

Conroy et al., 2001

Kenya 16%, diarrhea

Not Reported

Conroy et al., 1999

Kenya 9a/26b, diarrhea

Not Reported

Conroy et al., 1996

aTotal diarrheal diseasebSevere diarrheal disease

Household or POU Water Treatment by Solar Cooking or Solar Thermal Effects

• Heat to >60oC in black or opaque vessels (e.g., cooking pots)• Solar cooker or reflector increases temperature to65oC• Water and other liquids are pasteurized; most enteric viruses,

bacteria and parasites are rapidly inactivated• Where now used, it is practical, accessible and affordable• Low cost solar reflectors or cookers can be made from simple

& economical materials: cardboard and aluminum foil.• Only small volumes (10 L) can be exposed conveniently at

one time per water container and solar reflector • In many regions of the world, sunlight conditions are

suitable; approximately 200-300 days per year.

Physical Removal Processes for Household Water Treatment: Applications and Issues

Treatment Method• Plain Sedimentation• Filtration Methods:

– Rapid granular media– Slow sand filter– Ceramic filter– Fabric, paper & fiber

– Membrane filters

Microbial reductions• low (<90%)

• 90-99%• High (>99%)• Potentially high• Potentially high

– Depends on microbe & pore size• High

– Depends on microbe and pore size

Filtration Technologies for Household Water Treatment: Issues and Special Concerns

• Some simple, accessible, low cost technologies are:– not efficient for microbial removal: rapid granular filters – efficient only for some microbes

• paper, membrane or fabric filters for guinea worm– a key intervention but not applicable to all microbes

• Some simple, low-cost technologies may not be accessible or are of uncertain efficacy (ceramic filters)

• Some effective technologies (capable of efficient microbial removal) are inaccessible to many households– Complex, expensive and only externally available (microporous

membranes)– Some simple and effective technologies are unsuited to household use due

to their scale and O&M needs (SSF)

Physical Treatment Technologies for Turbidity Reduction in Household Waters: a Special Need

• Waters collected for household use may be highly turbid– Interferes with disinfection

• physical shielding/protection of microbes• disinfectant demand or consumption

– Contains pathogens and other microbes– Microbial regrowth– Aesthetics

• Turbidity reduction by physical or chemical methods ofen needed to prior to household disinfection

• Sedimentation and several filtration methods recommended– rapid granular media, fiber, cloth, membranes – possibly SSF, but less amenable to household use

Chemical Methods for Household Water TreatmentMethod Availability and

Practicality Technical Difficulty

Costa Microbial Efficacyb

Coagulation-Flocculation or Precipitation

Moderate Moderate Varies Variesc

Adsorption (charcoal, carbon, clay, etc.)

High to moderate

Low to moderate

Varies Varies with adsorbentd

Ion exchange Low to Moderate

Moderate to high

Usually High

Low or moderate

Chlorination High-Moderate Low-Moderate

Moder-ate

High

Ozonation Low High High High Chlorine Dioxide Low Varies High High Iodination (elemental, salt or resin)

Low Moderate to High

High High

Acid or base Rx with citrus juice, hydroxide salts, etc.

High Low Moder-ate

Varies

Silver or Copper High Low Low Low Combined Rx: coagulation- flocculation, filtration, chemical disinfection

Low-Moderate Moderate to High

Moder- ate

High

Chemical Methods for Household Water Treatment; Coagulation, Adsorption & Ion Exchange

• Coagulation-Flocculation (Sedimentation):– Inorganic coagulants (alum, iron, etc.)– Seed extract coagulants– Not recommended: due to required technical skill, lack of process control

tools, lack of material availability and variable efficacy• Adsorption: clay, activated carbon, charcoal and crushed organic matter

– Not recommended due to poor and variable performance and lack of process control monitoring tools

• Ion Exchange– Not recommended due to lack of availability, cost, lack of process control

monitoring tools

Candidate Chemical Disinfectants for Household Water Treatment

Disinfectant Recommended?• Free chlorine, Na or Ca OCl- Yes• Electrochemical oxidant fr. NaCl Yes• Chloramines No• Ozone No• Chlorine dioxide No• Acids (lime juice and strong acids) No* • Chemical coagulation + free chlorineYes

(commercial products)* except lime juice on emergency basis for cholera

Household Chlorination Interventions:CDC Safewater Intervention and Similar Systems

• Bottles of free chlorine solution (0.25-1%)• Commercial source (Na or Ca OCl-)• Electrolysis of NaCl (on-site)

– Generator located in community– Operated by a trained, local worker

• Replenish solution regularly (e.g., weekly) • Cap used as a measuring device• Add chlorine solution to household water

container (improved storage vessel)• Free Chlorine Doses:

– between 1-5 mg/l

Behavioral and Educational Components of the Household Chlorine Interventions

Behavior change techniques: • social marketing• community mobilization• motivational interviewing• communication• educationIncrease awareness of the link between contaminated

water and disease and the benefits of safe waterinfluence hygiene behaviors including the purchase

and proper use of the water storage vessel and disinfectant.

Chlorination and Safe Storage of Household Water:Disease Reduction and Microbial Quality Improvement

Loca- tion

Water Treatment Storage Vessel

Disease Reduction (%) Significant Microbe Decrease?

Inter-ven-tion

Reference

Saudi Arabia

HH Free Chlorine

Tanks Outside

48%, diarrhea Yes, E. coli +ive from 100-3%

W Mhafouz et al, 1995

India HH Free Chlorine

Earthen-ware

17-7.3%, cholera Not Measured W Deb et al., 1986

Bolivia HH Electro-chemical Oxidant

Special Vessel

44%, diarrhea Yes, E. coli +ive from 94 -22%;

Median E. coli from >20,000 to 0

W +

SH

Quick et al., 1999

Bangla-desh

HH Free Chlorine

Improved Vessel

20.8%, diarrhea Yes, E. coli +ive from 55 -13%;

Geom. Mean E. coli fr. 4.1 to 0.7

W Handzel, 1998; Sobsey et al.,

2003

Guinea-Bisseau

ORSf/ Free Chlorine

Special Vessel

No Data Yes, mean E. coli from 6200 to 0/100 ml

W +

SH

Daniels et al., 1999

Chlorination and Safe Storage of Household Water:Disease Reduction and Microbial Quality Improvement

Loca- Tion

Water Treatment

Storage Vessel

Disease Reduction

(%)

Significant Microbe

Decrease?

Inter-ven-tionc

Reference

Guate-mala

Street-vended

Free Chlorine

Special Vessel

No Data Yes, E. coli +ive from >40 to

<10%

W +

SH

Sobel et al., 1998

Zambia HH Free Chlorine

Special or Local Vessel

48%, diarrhea

Yes, E. coli +ive from 95+ to

31%

W +

SH

Quick et al., 2002

Mada- Gascar

HH Free Chlorine; (tradition

al vessel)

Special and

Tradi-tional

Vessels

90%, cholera, (during

outbreak)

Yes, Median E. coli from 13 to 0/100

ml

W +

SH

Mong et al. 2001; Quick,

pers. commun.

Uzbek-istan

HH Free Chlorine

Special Vessel

85%, diarrhea

No (small no. samples)

W

Semenza et al., 1998

Pakis-tan

HH Free Chlorine

Special Vessel

No Data Yes Thermotol. Colif. 99.8%

W +

SH

Luby et al., 2001

Effectiveness of combined coagulation-flocculation-sedimentation-filtration systems

• Effective (>99.9%) reductions of viruses, bacteria and parasites in lab studies with different waters

• Effective (>99%) reductions in indicator bacteria reductions

• Intervention studies document (22-26% and 38-50%) reductions in household diarrheal disease in intervention groups compared to control groups– PUR system

• Procter & Gamble and CDC studies

Cost Estimates per Household for Alternative Household Water Treatment and Storage Systems (US$)

System Imported Items Initial cost of hardware (per capita; per household)

Annual operating cost/capita and /household

Boiling None None (assumes use of a cook pot)

Varies with fuel price; expensive

Ceramic filter Filter candles $5; $25 $1, $5 for annual replacement SODIS and SOLAIR (solar disinfection by UV radiation and heat)

None (assumes spent bottles available)

Cost of black paint for bottles or alternative dark surface (roofing)

None

Solar heating (solar disinfection by heat only)

Solar cooker or other solar reflector

Initial cost of solar cooker or reflector & water exposure and storage vessels

Replacement costs of solar reflectors and water exposure and storage vessels

UV Lamp Systems UV lamps and housings Initial cost of UV system: US$100-300), $20-60

Power (energy); lamp replacement ($10-100) every 1-3 years

On-site generated or other chlorine and narrow-mouth storage vessel ("US CDC Safewater" system)

Hypochlorite generator and associated hardware for production and bulk storage

$1.60; $8.00 $0.60/$3.00 (estimated by US CDC); costs may be higher for different sources of chlorine and for different water storage vessels

Combined coagulation-filtration and chlorination systems

Chemical coagulant and chlorine mixture, as powder or tablet

Use existing storage vessel or buy special treatment and storage vessels (US$5-10 each)

Chemical costs ca.$US5-6 per capita per year ($26 per household per year, at 4 liters per capita (20 liters per household)/day

Summary and Conclusions• Results clearly document that simple systems of manually

treating collected household water and storing it in a safe vessel significantly improves microbiological quality and reduces waterborne diarrheal disease risks– Solar disinfection with UV and heat– chlorination and storage in an improved vessel– Combined coagulation-flocculation-sedimentation and filtration

systems (commercial products)• System fulfill (exceed) the requirements of an appropriate

global intervention to reduce disease burden because diarrheal disease is reduced by >5%

Summary and Conclusions

• Systems are being accepted, used, and considered affordable by participants based on:– Compliance– Acceptability– Willingness to pay studies

• Sustainability and dissemination still uncertain at present– Need follow-up studies to document sustainability and to

identify reasons for lack of it– Need approaches and systems to achieve sustainability

Research and Demonstration Needs• Several effective technologies in principle have not been

adequately evaluated for microbial efficacy and waterborne disease reduction in the field:– Solar cookers and reflectors– UV with lamps– Ceramic filters– Granular medium filters

• Alone• With chemical (e.g., chlorine) disinfection

– Combined chemical coagulants and chlorine• Limited data now becoming available; very favorable results

Next Steps • Recognize and promote the message that household and

other local water interventions are effective and deserve equal consideration with other interventions

• Consensus-building on most effective systems • Technical training and “how to” educational materials• Economic and policy analyses• Development of infrastructures and policies to disseminate

accepted and proven technologies• Creation and implementation of an international movement• Financial and other resources needed for a large scale and

sustained initiatives• Linkage to and integration with related elements of the

water and sanitation movement

WHO Guidelines for Drinking-water Quality, 3rd Ed. Microbiological Issues for Non-piped Supplies

• Encourage implementation of guidelines for systems to improve microbiological quality of non-piped household water and reduce waterborne infectious disease

• Provide guidance on and describe systems for safe collection, treatment and storage of non-piped household water

• Communicate the documented evidence that these systems reduce diarrheal and other waterborne infectious disease

Household treatment works and is included in the next WHO “Guidelines for Drinking Water Quality”

Further Information• Household chlorination and improved storage vessel

system: www.cdc.gov/safewater• SODIS: www.sodis.ch

• Critical review on household storage and treatment:Managing Water in the Home: Accelerated Health Gains

from Improved Water Supply, WHO/SDE/WSH/02.07, World Health Organization, Geneva, 2002

http://www.who.int/water_sanitation_health/Documents/WSH0207/WSH02.07.pdf