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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
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