Transcript Water Drinking Water Sources and their Risks

Drinking Water Sources and
Storage
ENVR 890
Mark D. Sobsey
Spring, 2007
WHO Risk-based Framework
Water Sources and Water Treatment
• Drinking water should be essentially free of disease-causing microbes,
but often this is not the case.
– A large proportion of the world’s population drinks microbially contaminated
water, especially in developing countries
• Using the best possible source of water for potable water supply and
protecting it from microbial and chemical contamination is the goal
– In many places an adequate supply of pristine water or water that can be
protected from contamination is not available
• The burden of providing microbially safe drinking water supplies from
contaminated natural waters rests upon water treatment processes
– The efficiency of removal or inactivation of enteric microbes and other
pathogenic microbes in specific water treatment processes has been determined
for some microbes but not others.
– The ability of water treatment processes and systems to reduce
waterborne disease has been determined in epidemiological studies
Source Water Protection:
Water Resources Management
• Integral to the preventive management of drinking-water
quality.
• Preventing microbial and chemical contamination of
source water is the first barrier against drinking-water
contamination of public healthconcern.
• Water resource management and potentially polluting
human activity in catchments and aquifers influence
water quality.
• This impacts treatment steps required to ensure safe
water
• Preventive action may be preferableto upgrading
treatment.
Influence of Land Use on Water Quality
• Assess land use influence on water quality
• Not normally undertaken by health authorities or drinkingwater supply agencies alone
• Establish close collaboration between public health authority,
water supplier and resource management agency
– may include other sectors, .e.g., agriculture, traffic, tourism
or urban development.
• National authorities must interact with other sectors to
formulate national policy for integrated water resource
management
• Set up regional and local structures to implement policy
– National authorities need to guide regional and local
authorities by providing tools
Land Uses to Consider that Influence Water Quality
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land cover modification
extraction activities
construction/modification of waterways
application of fertilizers, herbicides, pesticides and
other chemicals
livestock density and application of manure
road construction, maintenance and use
various forms of recreation
urban or rural residential development
– Pay particular attention to excreta disposal,
sanitation, landfill and waste disposal
other potentially polluting human activities, such as
industry, military sites,
Drinking Water Sources
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Ground Water
Surface water
Rainwater
Condensed water from the atmosphere
Reclaimed wastewater
Other?
Groundwater
• Water table or surficial aquifer
– First water encountered through the
soil or subsurface
– Often subject to contamination from
the land surface
• Confined aquifer
– Water found below a confining
subsurface later of clay, rock or other
impervious material
– Often protected from contamination
lan surface
• Both may contain geological
chemical contaminants
– Arsenic and fluoride are probably of
most health risk
• Confined aquifer water is often
better protected from surface
contamination
Surface Waters
• Lakes, ponds and other and “confined” bodies of
water
• Rivers, streams, creeks and other flowing bodies
of water
• All are subject to direct contamination from
wastewater and excreta discharges
• All are subject to contamination from land runoff
• Surface water should be assumed to be
contaminated unless proven otherwise by direct
and indirect evidence from observations and
analysis
Rainwater
• Rainwater as it falls from the sky is
essentially free of pathogens and toxic
chemicals
• Airborne contaminants can cause low
level contamination with microbes and
chemicals
• Rainwater is collected primarily on
roofs or other impervious collectors
– Contamination from roof/impervious
surface chemicals and microbes is
possible
• Rainwater is often stored in barrels,
cisterns and other surface and subsurface collectors or impoundments
– Contamination is very likely unless
special precautions are taken to
protect the collected water from fecal
and other sources of contamination
Condensed water from the atmosphere
• Atmospheric water as
clouds, fod and
airborne mist can be
harvested at it impacts
impervious surfaces.
• Solar Stills
– Water evaporated from
standing water also
can be condensed and
harvested
– Solar condensers
collect evaporated
water
– Solar energy can
supply heat
Reclaimed Water
• Water can be purified from sewage and other
wastewater
• Reuse for non-potable purposes in encouraged
• Reuse for potable purposes is discouraged
– Indirect reuse is considered feasible and of less risk
by recharging aquifers or reservoirs and allowing
addition die-off and further treatment
• WHO and countries have regulations for nonpotable and potable reuse
Water Treatment Processes: Storage
Reservoirs, aquifers & other systems:
– store water
– protect it from contamination
• Factors influencing microbe reductions (site-specific)
– detention time
– temperature
– microbial activity
– water quality: particulates, dissolved solids, salinity
– sunlight
– sedimentation
– land use
– precipitation
– runoff or infiltration
Larger Scale Water Storage
• Reservoir
impoundments and
other water storage
diversions
• Tanks and other
fabricated vessels
– Above and below
ground cisterns,
reservoirs and tanks
Household Water Containers for Safe Storage:
• Material: Depends on Rx; easy to clean;
lightweight, durable, impact- and oxidationresistant, 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
Characteristics of Preferred HH 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
Plastic vessels are commonly used – many have safe features
Properties
Composition
Volume (L)
Durability
Cleaning Ease
Lid
Faucet
Inside Cleaning
Chemical Dosing Ease
Cost
Distribution Cost
CDC Vessel
Plastic
(HDPE)
20
Good
Yes
Yes
Yes
Yes
Very easy
Med.-High
High
Jerry Can
Plastic
Oxfam
Plastic
Varies
Acceptable Good
Yes, qualified
Yes
No
No, usually
Easy (may be variable)
Low
Low, if local
14
Traditional vessels, such as pots,
urns and bowls can be made safe by
covering and providing a dispenser
(spigot or spout)
Yes
Yes
Yes
Yes
Very easy
Med.-High
High
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
Storage
Vessel
Storage
Times
Rural
Bangladesh
Water jars
1-2 days
Calcutta,
India
Widemouth vs.
narrownecked
Clay jars
("zeers") in
homes, etc.
Not
reported
Not measured
2 days to
1 month
Rural
Malawi
Stored HH
water;
others
South
Sudan
Rangoon,
Burma
Not
reported
Buckets
Khartoum,
Sudan
Microbial
Quality
Impact?
Increased V.
cholerae
Disease Impact?
Reference
Incr. (~10X
higher) cholera
rates
4X higher cholera
infections w/
wide-mouth
Spira et al.,
1980
Not Measured
Hammad
and Dirar,
1982
Not
reported
Incr. Fecal
indicators w/
time, summer,
w/ dust events
Higher fecal
coliforms
Not measured
Not
reported
Up to 2
days
Increased fecal
bacteria levels
Higher FC than
source
Not Measured
Lindskog
and
Lindskog,
1988
Mascher et
al., 1988
Han et al.,
1989
Not Measured
Deb et al.,
1982
Increased Microbial Contamination (Decreased Microbial Quality) and
Infectious Disease Risks from Inadequately Stored Household Water
Location
Storage
Vessel
Urban slum
and rural
villages,
Liberia
Kurunegala,
Sri Lanka
Storage
Times
Large
containers,
open or
closed
Earthen
pots and
others
Rural Africa Traditional
& metal jars
Rural
Various
Malaysia
containers
"A long
time"
Trujillo,
Peru
Not
reported
Widemouth
containers
Not
reported
24 hours
or more
Not
reported
Microbial
Quality
Impact?
Higher enterobacters in
stored than
source water
Higher FC in
stored
unboiled water
Higher TC and
FC
Higher FC in
unboiled than
boiled water
Higher FC in
stored than
source waters
Disease Impact?
Reference
Not Measured
Molbak et
al., 1989
Not Measured
Mertens et
al., 1990
Not Measured
Empereur et
al., 1992
Knight et al.,
1992
Higher diarrhea
risks stored in
wide-necked than
narrow-necked
Increased cholera Swerdlow et
risks
al., 1992
Reservoir Water Storage and Microbial Reductions
• Microbe levels reduced over time by natural
antimicrobial processes and microbial death/die-off
• Human enteric viruses in surface water reduced 4001,000-fold when stored 6-7 months (The Netherlands)
– Indicator bacteria reductions were less extensive,
probably due to recontamination by waterfowl.
• Protozoan cyst reductions (log10) by storage were 1.6
for Cryptosporidium and 1.9 for Giardia after about 5
months (The Netherlands; G.J Medema, Ph.D. diss.)
– Recent ICR data indicates lower protozoan levels in
reservoir or lake sources than in river sources;
suggests declines in Giardia & Cryptosporidium by
storage