The Basics of UV
This outlines the basic method for
disinfection but minor
adaptations might be necessary due to local conditions:
1. Water should be placed in
or glass bottles with secure tops. Plastic bottles are best
because they are widely used in developing
and often discarded as litter. Plastic bottles
are also safer for children to handle and transport
The bottles should be cleaned thoroughly and
any labels removed. Ideal bottle volume
1 to 2 liters, any larger is not as effective
because there is too much water for the
to penetrate sufficiently.
in Action - northern Brazil
2. Water that is cloudy or turbid should not be used.
dark print should be legible when held
behind the filled bottles. Turbid water can
poured in another vessel and allowed to settle.
The clear water can then be poured into
for disinfection. If the settling method does not
remove the turbidity, the water can be
through cloth or clean sand.
3. Aerated water facilitates disinfection so an inch of air
be left at the top of the bottles, the
top secured tightly, and then the bottle
be shaken vigorously for 15-30 seconds. The air
makes the viruses and bacterias more
soluble and therefore more easily disinfected by UV.
4. The bottles should then be placed in full sun. Good
include on a roof or a piece of
corrugated metal. The duration of exposure is
on the amount of UV that is available.
Many of these factors are listed below.
time frames are 6 hrs for up to 50% cloud cover and
2 days for 100% cloud cover. If the water
reaches 50 degrees Celsius only 1 hr is required.
While any clear container will work the type selected will have an
on the methods efficiency. Polyethylene
Terephtalate or PET plastic containers are preferred to PolyVinyl
or PVC containers. This is because PVC
containers have more UV-stabilisators than PET containers. To determine
a container is PET or PVC can be
relatively simple. PVC containers often have a blue tint and have a
smoke smell if burnt. PET containers
smell sweet when burnt (we don't recommend burning plastics and
inhaling the smoke).
Selected bottles should have a water depth of 6 - 10 cm, at higher
UV intensity is greatly reduced. Bottles
should be selected that have high surface area to depth ratios.
The bottles must also be replaced periodically . Scratches to the
will reduce the UV transmittance of the
container. Also UV light causes photoproducts to form on the outer
of plastic containers. These photoproducts
present no harm themselves but will reduce the amount of UV light
to the water.
If bottles are not available clear plastic bags with good seals can
used effectively. Pans or plastic puddles can also
be used as a replacement for bottles.
Should I Use UV Disinfection
for My Water? ...Factors Affecting UV
1. How is the weather? - Cloud cover reduces UV intensity approximately
same as sunlight intensity, so if the clouds are
blocking about half the full intensity of the sun,
you should leave your bottles out twice as long. If you live in a
rainy climate UV disinfection of water probably
isn't for you.
2. What season of the year are you in? - UV intensities are typically
summer and weakest during winter.
In winter months, leave the bottles in the sun 1.5
times longer than in the summer.
3. Where do you live? - UV intensities are greatest near the equator,
so if you live by the arctic circle you might want to
consider a different method for purifying your water.
4. What time of day is it? - UV intensity is greatest around midday, so
bottles should be put out in the late morning and
harvested late afternoon.
5. Elevation - higher elevations receive more UV radiation due to
atmosphere, so if you are living on a volcano or
on a mountain near the equator you are ready to go!
6. Ozone thickness -
based on time of year and global position
to the Process:
While the method described above works very well to remove bacteria and
from drinking water the
effectiveness of removal of some types of cysts and worms is still
The process also does not remove
chemical contaminants, pesticides, or heavy metals. If these
are present other treatment options
should be explored or alternate water sources should be found. It can
be stressed enough that highly turbid or
cloudy water will not be treated properly by this method.
More information about this bottle UV treatment method can be
at the following sites:
The Global Research Institute