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Safe Water System (SWS) Publications - FAQ Sheet
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FAQs |
Project Planning
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Safe Water Vessels
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Disinfectant
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Project Planning |
1.
What steps are involved in initiating a SWS
project?
Beginning a SWS project involves investigating
the various options for chlorine and vessel
production, identifying the target population,
and conducting focus groups in that population
to determine whether water quality and diarrhea
are priority concerns. It is also important
to determine the main forms of communication
in the population, and determine leadership
and community organizations. Additional themes
that it is important to explore in a prospective
project population include: current water
sources; attitudes toward the quality of
source water; treatment and storage practices;
and awareness of the role that contaminated
water can play in the transmission of disease.
Extensive information on these stages is
available in our Handbook PDF
5.09MB for large-scale projects and
in our Small
Projects Fact Sheet for smaller projects.
2. Does
CDC provide funding for SWS projects?
Unfortunately, CDC does not have funds
available to provide financial support for
the implementation of projects. However,
we will help interested organizations to
identify potential funding sources and provide
advice for writing applications for funding.
A list of potential donors is included on
our References
and Resources page, and we encourage
interested groups to look for funding from
sources they are familiar with. In addition,
we can provide technical assistance to projects
via our web page, telephone, and email support.
3. How does CDC support
SWS projects?
CDC's role in all of the SWS
projects is to provide technical assistance.
If funding is not available we provide assistance via our web page, telephone
conversations, and email support. If funding is available, we can travel
to project sites and provide assistance locally. We can meet with government
representatives and work with local producers to start production of the
bleach and safe water vessels. We can help with project implementation
and training. We can complete epidemiological
surveys or water quality analyses. We can
also complete a field trial of the intervention,
which includes a baseline survey about water
and sanitation knowledge, attitudes, and
practices, implementation of the intervention
in a targeted population, and then a study
of product adoption and the impact of the intervention on water quality
and diarrhea rates.
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Safe
Water Vessels |
1.
Does my project need to use the CDC safe
water vessel?
The CDC safe water vessel was
designed to provide an ideal safe water
storage container: robust, easily carried
(with hands or on head), of a size to provide
safe water to a family of 6-8 per day,
with an opening large enough for filling
but small enough to prevent contamination
of the water from hands, and a spigot that
can be also be used for handwashing. However,
we recognize that the CDC vessel is not
ideal for everyone. Because it is bulky,
the cost of shipping is prohibitive in
some areas. In addition, some projects
do not have the funding needed to create
a new vessel, and would prefer to use existing
water storage containers. For more information
on vessel options, please see the Other
Options question
below.
2. How much do the molds
for the safe water vessels cost?
If you decide
to use the CDC safe water vessel, you
can either make them in-country, or import
them from a country that already has a
mold and makes them for export. If you
choose to make the vessels in-country,
you would need to purchase the molds for
the plastic manufacturer to use. The most
inexpensive molds we have found are in
India, and the total cost for the 3 molds
(vessel, spigot, and cap) is approximately
US$15,000.
3. How much do the vessels
themselves cost?
The cost to produce the CDC
vessels in South Africa is approximately
US$2.50. In Zambia, it costs US$5 to
purchase and ship one vessel from South
Africa, where they are produced. In India,
where the vessels are made in-country,
it costs about US$2 to produce and ship
one vessel within the country.
4. What plastic is used in
the CDC vessel, and is it safe?
The CDC vessel
is made out of high density polyethylene
(HDPE). Plastic pipes and containers
have been used for many years to transport
and store chlorinated drinking water. To
our knowledge, it is safe to store chlorinated
drinking water in HDPE. We will stay
abreast of any emerging research into this
topic.
5. Have you received feedback
about the size of the vessel?
We have found
that 20 liters is an optimal size.
This is small enough to carry (via the
handle or on a head), but large enough
to provide enough drinking water for
a 6-8 person family for one day. Some
projects have asked for smaller vessels,
for example for agricultural workers
to carry into the field with them, and
others have requested larger containers
that require less frequent filling, but
we have found 20 liters to be the optimal
compromise. If the dosing of the sodium
hypochlorite is adjusted, a vessel of
any size can be used with the SWS project.
For more information on what to do if
commonly used storage vessels in a project
area have variable sizes, see question
eight in this section.
6. What are other options
for a vessel?
There are a number of vessel
options.
- First, you could determine whether
narrow-mouthed storage vessels, such
as jerry cans, are available in your
location and promote their use.
- Second,
if no narrow-mouthed vessels
are available in your location, or
if your populations do not have
the means to purchase an improved vessel,
you could simply recommend
that your population add the hypochlorite
to whatever vessel they currently
use. This has the benefit of
low cost. The main drawbacks of this
approach are: the use of vessels
that permit the easy contamination
of stored water, the continuation
of practices that can result
in contamination, such as dipping water
out of the top of a bucket, and difficulty
in establishing a hypochlorite
dosing scheme in the event of different
sized vessels.
- A third option is the
investigate the types of containers
currently used in the community
and determine if one can be modified
with a tap and a cover.
- A fourth
option is to use 15 or 20-liter
plastic buckets modified with
a lid and a tap.
- A fifth option is to import
the Oxfam safe water container.
Please see our small
project page for more detailed information
on all of the options included here.
7. Do you have any experience
with earthenware vessels?
We conducted a study in
Kenya that showed that if you treat water
with a higher dose of chlorine, the clay
pots can maintain an effective chlorine
residual for up to 24 hours. The clay pots
need to be kept clean and people need to
do their best not to touch the water with
their hands when they get remove water.
They should also use a clean cup or dipper
to remove the water. In Kenya clay pots
with fitted lids and spigots are produced,
and we are promoting their use.
8. What do you recommend
for dosing water if the water storage vessels
used within the project area vary?
There are
three main options. One option is to
incorporate a dosing scheme into the cap
of your hypochlorite bottle. In India,
the cap of the bottle has three lines on
it that indicate how full to fill the cap
based on three common storage vessel volumes.
This adds a small amount to the cost of
the hypochlorite bottle, but it increases
the likelihood that users do not need to
purchase a special vessel, which means
the project as a whole is less expensive.
A second option is to use a dropper bottle
that provides more flexibility in dosing.
Dropper bottles are used in the Piyush
project in Nepal. The third option is to
introduce a new, standardized vessel. There
are advantages to introducing a brand new
product that is identified with water storage
that can be marketed and used to educate
about safe water practices.
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Disinfectant |
1. Is sodium
hypochlorite (SH) the best disinfectant to
use?
Our investigations have shown sodium
hypochlorite to be effective and have broad
applications. We have investigated a number
of other disinfectants (calcium hypochlorite,
ozone, UV, solar disinfection) and treatment
processes (filters, slow sand filtration)
and feel that sodium hypochlorite offers
the best mix of low cost, ease of use,
safety, and effectiveness in areas where
there is enough water to drink and water
is not excessively turbid. We feel that these
characteristics are the reasons why most
water treatment systems in the US and Europe
have been using chlorine for disinfecting
drinking water for nearly 100 years. We do,
however, recognize that the other disinfection
methods noted above also effectively disinfect
water and are useful in a number of settings.
2. What about using HTH or chlorine tablets
instead?
Chlorine tablets and/or HTH (also
named calcium hypochlorite) are widely
available in some areas. We have found that
a number of potential users of the SWS know
that if they add the tablets to water, it
will disinfect the water. However, we have
also found that people have very different
ideas of the appropriate dosing and the tablets
vary in strength considerably. In Haiti,
a small saran wrap bag of approximately 100
HTH pellets is widely available and inexpensive.
However, the pellets are of varying size,
the quality of the pellets is unknown,
and depending on impurities in the manufacturing
process they can degrade quickly. In other
countries we have seen very high strength
tablets sold, which, if added to water
for disinfection would impart a strong, unpalatable
taste to the water. Thus, it is extremely
important to investigate the quality and
strength of the HTH or chlorine tablets,
and the appropriate dosing strategy before
attempting to use them for drinking water
treatment. For these reasons, we have found
that the hypochlorite solution is a better
option.
3. How do you ensure adequate shelf life
of SH?
Sodium hypochlorite is highly reactive and
volatile. At normal pH (6-8) sodium hypochlorite
can degrade substantially within 2-3 weeks.
This shelf life is not adequate for use
in the SWS, for the hypochlorite must remain
at high enough concentration to inactivate
disease-causing organisms. By raising the
pH of the hypochlorite solution, you stabilize
the solution. The pH can be raised by the
addition of sodium hydroxide, which is
widely available. In order to determine the
amount of sodium hydroxide to add to your
sodium hypochlorite solution, you will need
to complete trial-and-error testing. Add
a known volume of sodium hydroxide to a known
volume of sodium hypochlorite, and then measure
the pH with a meter or kit. Because source
water quality is different in each location,
there is not one standard volume of sodium
hydroxide to add to ensure pH is above 11.
You will have to start with a known volume
(perhaps 1 tablespoon in 1 gallon, or 5 ml
in 1 liter) and complete iterative trial-and-error
testing. The exact pH is not important in
this context - you simply need to ensure
that the pH is above 11.
4. Will adding NaOH change the effectiveness
of the SH?
No, because when the sodium hypochlorite
solution is added to water, the water decreases
the pH and the sodium hypochlorite more
active. The chemistry behind this is: the
pH scale is from 0 to 14. Acids have a pH
below 7, bases are above 7, and 7 is neutral.
Most natural water is around pH 6-7. When
sodium hypochlorite is in water, it breaks
up into two compounds, with the concentration
of each compound dependent on pH. One of
these compounds is significantly more reactive,
volatile, and more effective at inactivating
bacteria than the other. At high pH (above
11) the majority of the sodium hypochlorite
is in the form of the less-reactive compound.
Thus, when you add sodium hydroxide to
the sodium hypochlorite, you are converting
it into the less-reactive form. However,
water is around pH 6-7. When you add a small
amount (5 milliliters) of solution at pH
11 to a large amount (20 liters) of water
at pH 6-7, the mixture becomes pH 6-7. Thus,
when you add the hypochlorite at pH 11 to
your water in the SWS, you convert the hypochlorite
back into the reactive form, and then it
inactivates the disease-causing organisms.
5. Does the SH inactivate giardia and cryptosporidium?
Giardia
and cryptosporidium are both protozoa and
are resistant to chlorination because they
exist in water in a cyst form. The hard
coat of the cysts protects giardia and cryptosporidium
from being inactivated by chlorine. Cryptosporidium
is more resistant to chlorine than giardia.
See this inactivation table for more details.
Both protozoa, however, are fairly large.
Cryptosporidium is approximately 3-5 times
the size of the bacteria E. coli, and giardia
is approximately 5-10 times the size of
E. coli. Cryptosporidium and giardia can
thus be removed by filtration. If giardia
or cryptosporidium are a significant health
problem in the project area, a filtration
step (through ceramic, sand, or other filters)
can be added before adding the sodium hypochlorite.
The Safe Water System intervention has been
proven to reduce diarrhea in children, and
this intervention does inactivate many of
the ones that cause the most severe disease,
like cholera, dysentery, and typhoid fever.
6. What are disinfection
by-products, and are they an issue in the
SWS?
Disinfection by-products (DBPs) are chemical
compounds formed when chlorine is added
to water with organic material in it. All
natural waters have some organic material
in them, and generally waters that are
more turbid (dirty) have more organic material.
DBPs are a concern whenever chlorine is
added to drinking water, whether in the
Safe Water System or in a large-scale water
treatment plant in the United States, because
some studies have suggested that ingestion
of DBPs in water over a lifetime may be
associated with a very low risk of cancer.
However, this risk is very small (1 in
100,000 people over 70 years is what the
WHO considers when establishing their drinking
water guidelines (1996)). In areas where
many people, and many children, have diarrheal
diseases caused by unsafe drinking water,
the risk of cancer from THMs is miniscule
compared to the risk of death or stunting
from diarrheal diseases. The World Health
Organization is very clear on the importance
of microbiologically safe drinking water
(obtained by adding chlorine) as compared
to the risk from DBPs in their Guidelines
for drinking-water quality: "Where
local circumstances require that a choice
must be made between meeting either microbiological
guidelines or guidelines for disinfectants
or disinfectant by-products, the microbiological
quality must always take precedence, and
where necessary, a chemical guideline value
can be adopted corresponding to a higher
level of risk. Efficient disinfection must
never be compromised" (WHO Guidelines
for Drinking Water Quality, Volume 2, 1996).
Because the DBP question is often raised,
we have prepared two fact sheets on DBPs:
one is a short one-page document, and the
other is a more descriptive 6 page document.
7. If you add SH to water already treated
in a municipal water treatment plant, is
there a risk of a chlorine overdose?
This
is very unlikely. If sodium hypochlorite
is added to water that is already treated,
the water would most likely still be within
an acceptable range of chlorine residual.
Typically, chlorinated urban water systems
have free chlorine levels of around 0.1
to 0.5 parts per million. We calculate
our sodium hypochlorite solution dose to
give untreated water a free chlorine level
of around 1 part per million. So if you
add our solution (1 part per million) to
treated urban water (0.1-0.5 parts per
million), the level of the "overtreated" water
would still be in the acceptable range
of 0.5-2 parts per million (which is the
range that balances disinfection efficacy
plus reasonable taste).
8.
What happens if a child accidentally drinks
the SH?
A review of health effects from accidental
and intentional ingestion of sodium hypochlorite
(bleach) in Europe was published in 1994
by Proctor and Gamble in conjunction with
European poison control centers (Racioppi,
et al. Food and Chemical Toxicity, Volume
32, Number 9, pp 845-861). The results
of this review show that "acute accidental
exposure to household bleach in use or in
foreseeable misuse situations results, in
the great majority of the cases, in minor,
transient adverse effects on health".
The authors cited two studies specifically
on children: 1) A study in Chicago showing
that of 26 children admitted for accidental
bleach ingestion, only one had a moderate
health effect (irritation of the esophagus,
which healed on its own without intervention),
with the remaining children having only "minor
transient irritation effects", and 2)
A study of 23 cases aged 1 - 3 years, with
only one case having "superficial burns
in the esophagus", which disappeared
two weeks later. Suicide attempts in adults
have shown that a lethal dose of sodium
hypochlorite varies widely, with lethal
results at 200-500 mL of 3-12% strength.
It is important to remember that the concentration
of the SH used in the SWS is approximately
0.5-1.0 percent. In most countries, the
SH is sold in 250 ml bottles, but in some
500 ml bottles are used. The hypochlorite
ingested in the majority of the cases mentioned
above was full strength household bleach:
5 percent. Several factors make it unlikely
that the hypochlorite solutions recommended
in the Safe Water System could cause harm.
First, it is unlikely that a child would
accidentally drink 250 or 500 milliliters
of something that tastes as bad as the
sodium hypochlorite does. Second, based
on the data presented above, it is even
less likely, at the low concentration used
in this project, that anything harmful
would occur. However, we highly recommend
that part of the educational materials
emphasize the need to keep the sodium hypochlorite
solution stored somewhere safe (out of
sunlight, sealed, away from children) for
health reasons, to protect the sodium hypochlorite
from degradation, and to prevent spills
in households that have limited disposable
income to purchase more solution.
9. Which hypochlorite generator do you recommend?
A
number of companies manufacture hypochlorite
generators. Information on some of them
can be found in our small projects page.
There are several advantages in using a hypochlorite
generator. First, local production of the
sodium hypochlorite that minimizes transportation
costs. Second, in the event there is not
a reliable bleach producer in the country,
the hypochlorite generator provides that
capacity. Third, revenues from the sale
of the solution can be used to help support
operation and maintenance of the machine
and to pay the operator. Considerations
that must be taken into account when producing
bleach in this way include the need for
regular operation and maintenance of the
machine, payment of a reliable person to
operate and maintain the machine, replacement
of the cell of the generator every 5 years,
and the need for a reliable electricity supply.
10. Are there
advantages to having a private company
manufacture the SH?
There are several advantages to having a
company make the solution are: 1) Most likely,
all a company would need to do to make the
desired concentration of hypochlorite is
to dilute an existing bleach product. 2)
If demand for the solution grows, a company
is better able to expand production. 3) Many
companies have certification from Bureaus
of Standards for bleach products that can
often be applied to the new dilute solution.
4) Most reputable companis have quality control
procedures. In Madagascar, Rwanda, Kenya,
Malawi, India, Afghanistan, and Tanzania,
Populations Services International (a social
marketing non-governmental organization that
has successfully implemented a number of
SWS projects) has opted to have private companies
make the bleach for them.
11. What characteristics
are required for the SH?
First, it is important that the concentration
is correct (usually 0.5 to 1.0 mg/l). A concentration
that is too low requires too high a volume
to adequately treat enough water to be practical.
A concentration that is too high is difficult
to accurately dose, raising the risk of too
high a dose (which is unpalatable), or too
low a dose (which might not effectively disinfect
the water). Second, it is important that
pH of the solution is at least 11. This increases
the shelf life of the solution.
12. How much does
it cost to manufacture the SH?
In the first year of the country-scale project
in Zambia it cost US$78,000 to manufacture
400,000 bottles per year. The labor cost
was $23,000 and the materials (salt, vinegar,
bottles, and labels) cost was $55,000. The
total production cost was thus US$0.20 per
bottle, and assuming a family usage of one
bottle per month, the production cost for
a year's supply for one family is about US$2.40.
After the first year, costs are expected
to decrease. Costs vary by country, depending
on labor, materials, and value added taxes.
In small-scale projects using a local hypochlorite
generator and reusable bottles, the production
cost of the hypochlorite is only the cost
of the salt, water, labor, and electricity.
13. How do we determine the appropriate
SH dose?
The hypochlorite dose will depend
on the characteristics of the local water.
Usually an amount in the range of 5 to
10 milliliters added to 20 liters of water
is sufficient to inactivate the disease-causing
organisms, but not leave an unpleasant
taste. Once the size of the cap for your
project has been determined, some simple
experiments using the sodium hypochlorite
locally available, source water in your area,
and a kit that measures the amount of free
and residual chlorine can be used to determine
the appropriate dose. Please contact us at
safewater@cdc.gov for more information on
how to complete this testing.
14. What characteristics do you recommend
for the SH bottle?
We recommend the following
six characteristics for the sodium hypochlorite
bottle that is kept in the home: 1) The
size of the bottle should be between 250
and 500 milliliters. This is small enough
to be affordable and to ensure that the solution
will be used before it degrades, but large
enough that it will last a family for approximately
a month; 2) The neck of the bottle should
be compatible with soda bottle caps, which
tend to be mass-produced, are inexpensive,
typically have the desired volume of 5-10mL
for dosing, and are easily accessed in most
locations; 3) The volume of the cap should
be between 5 and 10 ml so that it can be
used to dose the solution; 4) The bottle
should be composed of an opaque plastic,
to prevent exposure of the solution to direct
UV radiation from sunlight, which will decrease
the shelf life; 5) A handle is not necessary.
This only increases the cost and decreases
the space available for instructions; and
6) The neck and cap should have at least
four threads to improve the seal. The cap
should have a raised ring inside to help
seal the bottle as well.
15. How can we
save money on manufacturing the SH bottle?
One way to save money when designing the
solution bottle is to design the bottle so
that an already locally available cap will
fit it. We recommend a plastic soft drink
bottle cap with a volume of between 5 and
10 milliliters. Using a locally available
cap will save you from having to purchase
a mold for the caps, and soft drink caps
are typically mass produced at very low cost.
The existing caps must fit tightly and securely
on the project bottle design, however.
16. What do we do if the source water is
turbid?
Water that looks dirty or cloudy is
called turbid water. Turbidity is a measure
of the amount of light that is scattered
as it passes through the water sample.
If more particles are in the water, more
light will be scattered, and the turbidity
is thus higher. Water that looks "dirty" will
have a higher turbidity than water that
looks clear. Turbidity itself is not a
problem, however turbidity is often used
to represent the amount of total suspended
solids and the amount of organic matter
in the water. There are two issues with
adding chlorine to water that has a high
turbidity: 1) Chlorine reacts preferentially
with organic matter before reacting with
bacteria. Thus, you need to make sure to
add enough chlorine to inactivate the bacteria,
2) There is a potential of creating more
disinfection by-products if there is a
higher concentration of organic matter
in the source water. There are three strategies
that can be used to make turbid water clear:
1) Filtering the water through a cloth
filter will remove some of the organic
matter; 2) Letting the water settle for
12-24 hours so the organic matter falls
to the bottom and then pouring off the
clearer water into a separate vessel will
also remove some of the organic matter;
or 3) Increasing the dose of sodium hypochlorite
solution adde d to the water to make sure
there is enough chlorine to inactivate
the disease-causing organisms. Because
every community is different, experiments
to determine which is the most acceptable
and appropriate strategy will need to be
conducted in the project community.
17. Why does free chlorine in treated water
decline over time?
Chlorine is an extremely
reactive chemical. Right after the sodium
hypochlorite is added to the water, chlorine
levels decline because the chlorine is
reacting with organic matter and microbes.
After those reactions are complete, chlorine
in water will slowly escape into the air
as a gas. This is the reason that free and
total chlorine levels slowly degrade over
time in a covered (but not sealed) container,
and also why we recommend that the pH of
the hypochlorite solution be raised to over
11 to extend the shelf-life before it is
used.
18. How can you distribute the SH throughout
the country?
In many projects, PSI has initiated
social marketing campaigns, which include
the activation of networks of wholesale
and retail outlets, facilitating distribution
to communities where vulnerable populations
live. For smaller projects, one idea is
to purchase space on private delivery trucks
that are already going to target locations
to deliver goods such as soft drinks and
beer, or to request a donation of space
by the private companies as a charitable
activity.
Top |
Behavior
Change |
1. What is social marketing?
Social
marketing is the practice of applying
marketing techniques to socially useful
products. Social marketing has been successfully
employed by Population Services International (PSI) to
disseminate the SWS in Bolivia, Madagascar, Zambia, Tanzania, Rwanda, Malawi,
Kenya, India, and Afghanistan. CARE Kenya
also successfully used a combined social marketing/community mobilization
approach to implement the SWS in Western Kenya (more
information). A case control study conducted during a cholera outbreak
in Fort Dauphin, Madagascar, where a campaign to socially market sodium
hypochlorite solution had been launched one month earlier, showed that
the risk of disease was substantially reduced in households using the disinfectant
solution. Take
a look 215KB at the full text of this paper.
2. What is
community mobilization?
Community
mobilization is a behavior change method
that is characterized by community
participation in the prioritization
of their problems, and the selection,
implementation, and monitoring of interventions.
In Madagascar, CARE applied the community
mobilization process to a target population
in the context of a social marketing campaign, and doubled the proportion
of households adopting the disinfectant solution relative to households
that were exposed to social marketing alone. CARE Kenya used community
mobilization combined with social marketing in a field trial of the SWS
in rural communities, motivating over a third of the target population
to adopt the disinfectant solution in less than 6 months. A health impact
study in the target population in Kenya revealed that children under 5
years old living in households using the SWS had a 58% lower risk of diarrheal
illness than children living in households not using the SWS.
Top
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Other |
1. How do I obtain
materials about the Safe Water System?
All
of the Safe Water System materials, including
our Handbook, published articles, and information
are available on-line at http://www.cdc.gov/safewater.
We also have published a CD-ROM that contains
the Safe Water System Handbook, our entire
web site, a video about our project, several
statistical software packages, and an epidemiology
self-teaching text. We also have hard copies
available of our Handbook (in English,
Spanish, French, and Arabic) and our published
materials. For copies of any of these materials,
please email safewater@cdc.gov.
2. Is there a cost associated
with any of the materials?
No. The Handbook,
CD-ROM, and shipping are all provided free-of-charge.
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Date:
July 24, 2006
Content source: National Center for Infectious Diseases
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