Safe
Water System Manual
5.0
Decide on products
Tasks:
A
Safe Water System project enables households to disinfect and store essential
quantities of household water in safe containers.
The
products ("hardware") of a Safe Water System include:
•
disinfectant solution and its container
• a vessel for safe water storage
in the home
• a filter, if local water is turbid
Project
planners must decide how these products will be manufactured or obtained. There
are a variety of ways to produce a disinfectant solution, and there are many different
safe water storage vessels.
5.1
Choose a production method for disinfectant
The
disinfectant should kill or inactivate pathogens that are likely to be present
in the water sources of the target population. An ideal disinfectant should:
•
be reliable and effective in killing pathogens under a range of conditions likely
to be encountered
•
provide an adequate residual concentration in the water to assure persistent disinfection
during water storage
•
neither introduce nor produce substances in concentrations that may be harmful
to health, nor make the water unsuitable for human consumption or aesthetically
unacceptable
•
be safe for household storage and use
•
have an adequate shelf life without significant loss of potency
•
be affordable for users
There
is no perfect water disinfectant that will work optimally under all circumstances.
Each has advantages and disadvantages.15 However, in our experience,
demonstration projects have identified chlorine, specifically 0.5% to 1% sodium
hypochlorite solution, as having the best overall characteristics for both production
at the local level and convenient dosing for household water disinfection. It
is also extremely inexpensive to produce, making it an affordable option for economically
disadvantaged populations. Sodium hypochlorite solution at this concentration
is also safe, with evidence that ingestion of sodium hypochlorite at 10 times
greater concentration causes no lasting damage.16
Sodium
hypochlorite has two disadvantages that must be addressed. The first is the issue
of taste. Some populations object to the taste of chlorine, which may decrease
use of disinfectant. Behavior change interventions should be designed to address
the issue of taste (see section 7.0). In Zambia, one
approach was to teach people to associate chlorine taste as an indicator of the
safety of drinking water. In Bolivia, an approach was to teach people to
treat water in the evening for the following day, so that the taste would dissipate.
The second disadvantage is the potential for degradation of chlorine concentration
during storage, particularly in hot climates. This problem can be mitigated by
alkalinizing the solution and by storing it out of sunlight in opaque containers
in the coolest possible place. In hot climates, the shelf life can be as little
as 1 month, but with alkalinization, the shelf life can be increased to 4 months
or more. In cool climates, the shelf life is greater than 6 months. Shelf life
must be determined in each new region because of variations in source water and
climate.
Another
concern about chlorination of water is the health effects of trihalomethanes.
Trihalomethanes are disinfection byproducts that are formed when hypochlorite
is used to treat water with organic material in it. Research suggests that, over
a lifetime, the risk of bladder cancer increases with chronic consumption of trihalomethanes.
In populations in developing countries, however, the risk of death or delayed
development in early childhood from diarrhea transmitted by contaminated water
is far greater than the relatively small risk of bladder cancer in old age.
There are alternative
safe and effective ways to produce sodium hypochlorite solution:
a)
local production from water and salt with a low cost hypochlorite generator that
is simple to operate
b)
production by an existing local or multinational business in country
For
the Safe Water System, we have decided against using dilute solution of calcium
hypochlorite from High Test Hypochlorite (HTH) powder because of the caustic,
hazardous nature of the highly concentrated (70%) powder. Also, in most countries,
HTH must be imported, and storage can be difficult, particularly in hot, humid
conditions.
Another
option that is not recommended is to promote use of a locally available commercial
bleach to treat water in the home because experience has shown that this approach
leads to problems with acceptance. Bleach bottles often display instructions to
use bleach to whiten clothes and clean toilets, which deters people from using
it to treat drinking water. Another problem with commercial bleach is that it
may contain additives or impurities and that concentration can vary, which makes
it more difficult to provide dosing instructions. It is best to create a new product
especially for treating drinking water.
Each
of the preferred options for production of disinfectant solution is described
below.
a)
Local production from water and salt with a low cost hypochlorite generator
that is simple to operate
Using
this method, an arrangement can be made to produce hypochlorite in the community.
Devices are available from several manufacturers that are designed to reliably
produce hypochlorite solutions through electrolysis of ordinary salt and water
(3% salt solution).7, 15,17 Most of these devices, called hypochlorite
generators, use electricity from an electrical grid, but solar powered hypochlorite
generators can also be used.
A
suitable place is required to operate the machine and store solutions. A two-person
team should be trained to operate and maintain the device and to monitor the hypochlorite
concentration. (See Annex C.)
There is a range of sizes and capacities of hypochlorite generators. Different
models can produce as little as 10 liters (enough for 40 families) per day up
to a maximum of 400 liters (for 1600 families) per day. Running 12 hours per day,
an electric-powered hypochlorite generator can produce enough disinfectant solution
to treat water for about 8,000 families (40,000 - 48,000 people) every 2 weeks.
Once
production starts, the disinfectant can be produced inexpensively by a community
worker. In Zambia, disinfectant sold for approximately $0.20 for a month's
supply for a family of 6 people. In Madagascar, disinfectant sold for $0.30
for 2 month's supply, and in Kenya, for $0.20 for 2 month's supply.
These prices did not take into account the cost of marketing and distribution.
Local production has been employed in Bolivia, Peru, Ecuador, Zambia, and Madagascar.
As the
water project expands to reach additional communities, it may be necessary to
obtain additional generators to meet increased demand and train more workers to
produce and bottle disinfectant.
b)
Production by an existing local or multinational business in country
With this method, a business such as a bleach manufacturer produces a disinfectant
product of a specified concentration. If an existing business can produce a suitable
disinfectant, the manufacturer is likely to have in place procedures for quality
control, bottling, labeling, and distribution. When the project is ready to expand,
the manufacturer can quickly increase production. This method has been used in
Kenya.
Problems
may arise, however, because the manufacturer, rather than the project administrators,
will control price and production. Business usually requires a certain profit
margin, which may make the disinfectant price too high for intended users. There
may be increased transportation costs, depending on the distance between the manufacturing
plant and the communities that purchase the product.
Figure
4: Comparison of methods for production of disinfectant solution
Disinfectant
production
options | Cost
of
Solution | Local
job
creation | Cost
of
transport | Quality
control | Efficiency
of
bottling,
labeling | Start-up
costs
and
staff
training | Ease
of
scaling up | Control
over
product
price
| Districution |
Local
production
with
appropriate
technology | Low | Good | Low | Good | Good | High | Good | Good | Network
must
be
developed |
Production
by
exisiting
company | Depends
on
negotiation | Depends
on
size
of project | Higher | Good | Good | Lower | Depends
on
capacity of
company | Poor | Existing
distribution
network |
5.2
Choose bottles for disinfectant solution
Disinfectant is
put into bottles that are then distributed to outlets and sold to households.
There are several issues to consider in the choice and design of a bottle.
•
Returnable or non-returnable bottles?
Returnable
bottles can save project costs and result in a lower price for consumers. When
the contents of a returnable bottle are gone, the consumer returns the empty bottle
to a sales outlet and gets a discount on a new bottle. Bottles are sent back to
the production point to be cleaned, relabeled and refilled. Returnable bottles
reduce the likelihood that empty bottles will become solid waste (although this
has not been a problem yet because people tend to reuse non-returnable bottles
for other purposes when the disinfectant bottle is empty).
Non-returnable sealed bottles have been preferred by social marketing NGOs because
they facilitate quality control and make operations logistically simpler.
•
Color
The
bottle should be opaque to extend shelf life.
•
Size
The
bottle should not be so small that new ones need to be bought too frequently;
nor should it be so large that the supply of disinfectant lasts longer than its
effective shelf life. Many projects have found that a 250 ml bottle works well,
as this is approximately the amount that an average household uses in 2 to 4 weeks.
Up to 500 ml volume is satisfactory in cool climates. In hot climates, the shelf
life is reduced, and 500 ml of disinfectant may begin to lose its strength before
it is used up.
•
Paper label to be attached or labels to be silk-screened (painted) on bottle?
The
bottle must have a clear label that identifies its contents and provides instructions
for use in households. Silk-screened labels wear off in time, so if bottles are
to be returnable, paper labels may be more practical.
•
Measuring cap
The
bottle's cap should be used to measure the correct amount of disinfectant to add
to the quantity of water in the recommended water storage vessel. Therefore the
size of the cap and instructions for its use must be designed with the water storage
vessel in mind. The dose must be determined using the locally available disinfectant
with the locally available water in the vessel recommended by the project because
different waters require different doses of sodium hypochlorite for adequate disinfection.
This
is best accomplished via trial and error, measuring free chlorine levels one half
hour after dosing. A qualified person can start by adding ½ or 1 capful,
then measuring the chlorine level, and then continuing to add increments of ½
or 1 capful to the vessel until the correct chlorine level is achieved in the
stored water. A free chlorine level of 0.5 to 2.0 mg/L is optimal. A cap should
facilitate measuring the correct amount of disinfectant for the water storage
container. For a 20-liter water vessel, the dose of disinfectant will likely be
between 5 and 10 ml, so a cap size of approximately 2.5 to 10 ml will work best.
•
How to produce or procure the bottle
The
project may be able to use a locally produced bottle of appropriate size with
an acceptable cap to which a label can be applied. However, there can be problems
with locally produced bottles. Sometimes bottles are proprietary and are therefore
not available for the project. Also, available bottles may be used for other products
such as chemicals, and consumers may mistake one for the other.
Another
option is to manufacture a unique bottle. A unique bottle has advantages in that
it can be developed to meet the exact specifications required (size, shape, cap)
and consumers will come to recognize it. A mold to produce a bottle is expensive
(for example, $8000 was the cost in Bolivia), but once produced, the project cost
per bottle may become less expensive.
5.3
Choose a vessel for water storage in the home
Virtually
every type of tank or container imaginable has been used for household water storage.
Unfortunately, most do not adequately protect water from contamination. Many are
open without lid or cover. Used 55-gallon oil drums and open plastic and metal
buckets are commonplace.
Many
people obtain or buy previously-used containers because they are cheaper. However,
sometimes these containers have held poisonous substances such as pesticides.
Families have become ill or have even died after drinking water stored in them.
Studies
have shown that even if water is microbiologically safe when put into such containers,
it can be quickly contaminated during storage and use, primarily by contact with
human hands or contaminated utensils that are used to withdraw water. Dust, animals,
birds and insects can also contaminate water when the vessel is inadequately covered.
Under these circumstances, even when water is initially disinfected, the subsequent
contamination is often so great that it nullifies the disinfectant. Water stored
in wide-mouth vessels (which allow stored water to be dipped out with hands or
utensils) is much more likely to be contaminated than water in vessels that must
be poured. Many studies have shown the importance of a suitable household water
container to prevent waterborne diseases.1, 18-21
 |  | |  |
Buckets
(plastic
or metal) | 55
gallon
oil drums | clay
pots | cooking
pots |
Typical
containers used for household storage that are often kept uncovered and do not
adequately protect water include:
In
many countries, clay pots are popular water containers with a history of use that
goes back generations. Many families prefer to use clay pots because they are
porous and permit evaporative cooling. They are also accustomed to the taste of
water in clay pots. In such cases, it may be difficult to convince people to change
to a different type of container. In Kenya research suggested that clay
pots may be reasonably effective storage containers, if kept clean, if people
avoid touching water when they dip it out (in some countries, spigots are placed
in clay pots to avoid this problem), and if the water is chlorinated when it is
put into the pot.
 |  |  |
| jerry
cans | plastic
bottles | picnic
coolers |
Commonly
used vessels for household storage which may adequately protect water if clean
and used correctly include:
CDC
and PAHO have designed a 20-liter, plastic vessel with a narrow mouth, lid, and
faucet. Recently, the design was improved with assistance from Procter and Gamble.
This vessel has been field tested in Bolivia and Zambia with good results. PAHO
Peru and PAHO Ecuador have employed containers with similar characteristics in
their projects. Oxfam has designed a bucket with a tightly fitting lid, a smaller
opening in the lid, and a spigot.
Below
are desired characteristics of a container that will prevent contamination of
contents and facilitate disinfection of water:
1.
Appropriate shape and dimensions with a volume between 10 and 30 liters so that
it is not too heavy, fitted with handles to facilitate lifting and carrying, with
a stable base to prevent overturning. If possible, a standard sized container
should be used because then dosing can be standardized. 20 liter vessels have
worked well in earlier studies. If children often carry water, the vessel will
have to be smaller or the child will need to collect water in a smaller container
and pour it into the safe storage container.
2.
Durable material, resistant to impact and oxidation, easy to clean, lightweight,
and translucent. High-density polyethylene (HDPE) is often the most appropriate
material that is readily available. HDPE should be specially treated with ultraviolet
absorbers, or exposure to sunlight over time will damage the plastic and vessels
will crack.
3.
An opening large enough to facilitate filling and cleaning but small enough that
even a child cannot easily insert a hand with cup or other utensil to dip out
water. The inlet should be fitted with a durable screw-on lid, preferably fastened
to the container with a cord or chain. A diameter between 6 to 9 cm is optimal.
4. A
durable spigot or spout for pouring that is resistant to oxidation and impact,
closes easily, and can discharge approximately one liter of water in about 15
seconds.
5.
Instructions for use of the container, disinfection of contents, and cleaning
the interior, permanently affixed to the container on material that does not deteriorate
when wet or moist.
6.
A certificate that indicates the container complies with requirements of the Ministry
of Health or an equivalent appropriate authority.
Figure
5: Comparison of possible vessels for water storage
| Vessel | Durability
Easy
to
clean | Lid | Faucet | Cleaning
inside | Volume | Ease
of dosing
with
disinfectant | Cost | Distribution
costs |
| CDC
vessel | Good | Yes | Yes
(durable) | Yes
hand can fit in opening) | 20
liter | Very
easy
(standard volume) | Moderate
to
high | Higher
(may
require import) |
| Acceptable
local jerry can (narrow mouth) | Fair | Yes | Usually
do not have faucets | Usually
not | Variable | Can
be more complicated (variable volume) | Low | Lower
because they are locally available |
| Oxfam
vessel | Good | Yes | Yes | Yes | 14
liter | Very
easy (standard volume) | Moderate
to high | Lower
(will require import) |
Figure
5: Comparison of possible vessels for water storage
In
most countries, the choice is between obtaining or manufacturing a specially designed
vessel with all or most of the characteristics above or promoting use of a locally
available vessel that has some of the desired characteristics.
A
vessel that is already available in communities will cost less but may be less
effective. A specially designed vessel will always have more of the desired characteristics.
Typically
most locally available vessels lack most of the desired features. Many local vessels:
•
have a mouth which is too narrow (difficult to clean)
•
have no top to keep out contamination
•
do not have a faucet
•
are less durable
•
vary in volume
Education
on how to properly disinfect water is much more complicated if households have
vessels of different design and volume. Mistakes adding the correct amount of
disinfectant are likely. If the vessel is smaller than the standard and the dose
is therefore too much, a bad taste results. If the vessel is larger and too little
disinfectant is added, the water is not effectively disinfected.
Education
on how to clean vessels must be tailored to the type of vessels used. If the opening
of the vessel permits the entry of a hand, then the vessel can be cleaned with
soap or detergent and water. If the opening is too narrow for the entry of a hand,
then instructions for cleaning must be adapted to local conditions. This is one
method that has been used:
•
Pour 1-2 liters of water into container
•
Add double the usual dose of sodium hypochlorite (e.g., 2 capfuls instead of one)
• Add
detergent
•
Add hard rice grains or gravel
•
Agitate vigorously
•
Pour out solution
•
Rinse
The
vessel is more suitable if it has more of the desired characteristics. Sometimes
no local vessels are acceptable (only buckets are available). If only buckets
or other "unacceptable" vessels are available and production or importation
of a specially designed vessel is not feasible, an alternative strategy would
be to locate or develop a secure cover for the bucket. Promotion and education
would address keeping the bucket covered and being careful not to let anyone's
hands touch the water. In Madagascar, this situation occurred in the early
stages of the project (before special vessels were obtained). Promotional material
stressed the importance of keeping the buckets covered and pouring, rather than
dipping, the water.
Inside
of Brochure from Madagascar...
How
to assess possible household water storage vessels:
If
your project is considering recommending a local vessel, search the community
for possible vessels in common sizes that are widely available and used in the
area. Then assess each for the characteristics discussed above. Use a worksheet
such as the one on the next page to help make a systematic comparison. There is
a blank copy of this worksheet in Annex D. On the next
page is an example showing how the worksheet was completed by some planners comparing
a specially designed vessel and three particular vessels that are commonly available
in their project area (earthenware jug, a plastic jerry can, a 10-litre bucket
with lid).
Figure
6: Example Worksheet for Assessing Possible Household Water Storage Vessels
|
Characteristics |
Specially
designed vessel | Common
earthenware jug | Plastic
jerry can | Bucket
with lid |
| Volume:
standard, 10-30 L, marked | Standard
20 liters | Varies
- 20-40 liters | Variable |
Standard 10 liters |
| Design |
Easy to carry,
stable | Familiar,
difficult to carry, stable | Easy
to carry, stable | Easy
to carry, stable |
| Material |
Plastic durable
& easy to clean | Breakable,
porous, holds pathogens, durable in households that take care of them |
Cannot see inside
- gets discolored |
Easy to clean |
|
Inlet
with screw-on lid; no access to dip with hands or cup |
Yes | Some
have lids placed on top. Dipping is usual practice |
Yes |
Usual
practice is to dip for bath |
|
Faucet or narrow
mouth to pour water | Faucet |
Not usually, but
in some countries clay pots are made with faucets |
Narrow mouth |
Wide mouth |
| Access
to inside for cleaning |
Yes - hand can reach in to scrub | Access
to clean | Difficult
to clean inside | Access
to inside for cleaning |
| Device
for measuring disinfectant | Can
be designed as part of vessel or disinfectant bottle |
Depends on site
- if clay pots have a standard size, dosing will be easier; very difficult to
design dosing if widely variable volumes |
Can design as part
of disinfectant bottle for two standard volumes of jerry can - - but measuring
mistakes possible | Can
design if bucket of standard size. Difficult if bucket sizes vary |
Figure
6: Example Worksheet for Assessing Possible Household Water Storage Vessels (continued)
|
Characteristics |
Specially
designed vessel | Common
earthenware jug | Plastic
jerry can | Bucket
with lid |
|
Instructions
for use, disinfection and cleaning affixed |
Can be standard
for standard volume; can affix before sale |
Must provide apart
from clay pot | Labels
can be produced for households, but must be affixed by owner |
Labels can be produced
for households, but must be affixed by owner |
|
Certification
of MOH | Can
be obtained and distributed with vessels |
Difficult to certify
used items already in the home | Difficult
to certify used items | Not
recommended for storage, therefore not certifiable |
|
Cost |
Expensive
but lasts long time | Cheap,
already present in homes |
Typically less expensive than special vessel; limited safe life; accessibility
varies by country | Cheap,
accessible |
| Other
comments | Attractive,
novel, status item | Familiar,
widely available | Likely
to be purchased used and contaminated; may be unsafe—need to assure that it is
not contaminated | Familiar,
widely available |
|
Performance
in field trials | Used
correctly, get improved water quality and decreased diarrhea |
Recent
studies suggest that can maintain chlorine residuals for up to 24 hours. |
Performed
OK in Zambia if had a lid | Performed
all right in Ndola, Zambia, if kept covered |
|
Overall assessment |
Best choice if
can obtain for project | If
other alternatives unfeasible, it may be possible to develop safe practices with
clay pots. | Has
drawbacks but acceptable if no other options |
Not ideal, but
acceptable if there are no other options and if a good, well-fitting lid is available |
Whether
a specially designed vessel can be used in a project depends on whether quantities
of such a container are manufactured regionally or locally, and whether the project
can afford to pay for them. Shipping a vessel long distances from point of manufacture
to users may cost as much as the vessel itself. Therefore, local or regional manufacture
of a specially designed vessel is important. Refer to the web site of the U.S.
Centers for Disease Control and Prevention (www.cdc.gov/safewater)
for the most current information on manufacturers of vessels and molds. In
Bolivia, a specially designed vessel was manufactured for $4.00. In
South Africa, the specially designed vessel sold for approximately $4.00.
Oxfam sold their vessel for approximately $3.50. See section 9.0 for more information
on production of vessels.
Important
decisions are based on the type of vessel used. For example, the dosing of disinfectant
depends on the volume of the vessel. Educational materials will need to address
advantages and disadvantages of the vessel. The manufacturer's cooperation will
be important to attach promotional information to vessel surfaces and to correct
any problems identified after vessels are being used.
5.4
Choose process or product to use if water is turbid
In areas where
water is turbid, pretreatment to filter out sediment can improve the aesthetic
quality of water and increase the efficiency of disinfection, and, in some cases,
reduce the degree of microbial contamination.22 The simplest method
is to filter water through locally available, inexpensive cloth such as sari cloth
(Bangladesh), or chitenge (Zambia). To make a filter, fold the cloth over a number
of times, enough to remove turbidity yet optimize flow. Do a trial with local
cloth and local water. The use of the cloth will need to be added to educational
messages, especially on the label of the disinfectant.
In
some regions with extremely turbid water, it may be difficult to adequately filter
water with cloth because the cloth can become clogged with organic material. In
such regions, it may be necessary to teach people to let water settle overnight
and then decant the cleared water into a new container. Alternatively, other filter
systems such as slow sand filters could be considered, although cost and complexity
are potential drawbacks.
Filtering Water with Cloth
Using
a Settling Technique
