Solar still built into a pit in the
ground
[[Image:Condensationpit.jpg|thumb|right|150px|Gathering water
through the use of a pit (or 'solar still') is a much touted
survival technique
1) Clear plastic sheet for cooling condensate.
2) Sheet anchor stones (in a shallow ditch).
3) Condensate runs along sheet to drip into can.
4) Collection can, at bottom of dug pit, holds condensate &
tube end.
5) Drinking tube from can bottom to outside still.
6) Soil or other material, containing all the water you hope to
drink.
-- Hints --
Often works better at night.
Make it as big as practical.
Plastic must be steep enough to run not drop, and not touch the pit
soil. ]]
A
solar still is a low tech. way of
distilling water, powered by the heat of the
sun (more precisely, the heat & humidity of
the soil, and relative cool of the plastic). Two basic types of
solar stills are box, and pit. In a solar still, impure water is
contained outside the collector, where it is evaporated by the sun
through clear plastic. The pure
water
vapor (and any other included volatile solvent) condenses on
the cool inside plastic surface and drips down off the low
point(pebble), where it is collected and removed. The box type is
more sophisticated.
Solar stills are used in cases where rain, piped, or well water is
impractical, such as in remote homes or during power outages.
In
Florida
and other hurricane target
areas that frequently lose power for a few days, solar distillation
can provide an alternate source of clean water.
Solar stills are occasionally used on a longer term basis in
developing world settings. However,
depending on environmental conditions, they usually produce a
relatively small amount of water, and even less where the source is
saline or
brackish. If the source is
inadequate, a compromise method is to mix the distilled water with
the brackish or saline water purified with other methods - this
gives a more adequate quantity and re-introduces the other source
contaminants, while still lowering the salinity, and improving the
taste.The Water Pyramid is a larger version, which uses an
inflatable dome as the condensing surface and can be used in
tropical, rural areas.
Knowing how to put together a solar still is often billed as a
useful
survival skill and could
provide an important means of potable water in the event of a
wilderness emergency. Nevertheless, under typical conditions
makeshift solar stills rarely produce enough water for long-term
survival, and the sweat expended in building one can easily exceed
its daily output. Solar stills can extract water from moisture in
the ground but to increase the amount of moisture available to a
solar still, water (fresh or
saline)
can be added inside or along the edges of the still. Where no water
sources are readily available, shredded vegetation , wet soil/sand,
urine or covered feces, can be used inside the pit. If only the
natural soil moisture is used, the pit must usually be moved as the
productivity drops. To prevent losing moisture by taking apart the
still to retrieve collected water a length of plastic tubing can be
used to sip water as it accumulates.
Alternatives
Besides using stills (which work by controlled evaporation and
condensation of water), filtration, and reverse osmosis are more
difficult but more productive. Water may thus be obtained from
other larger sources (eg the sea as well as fauna and flora, ...)
More information can be found at
Drinking
water.
See also
- Solar water
disinfection - uses the sun's infrared energy and heat to
disinfect water, but does not distill (evaporate and condense) the
water.
- Watermaker - A filter to obtain clean
water from seawater; used in large vessels
- Solar cooker -- A similar device
used to cook food.
References
Jackson, R. D.//van Bavel, C. H. M. (1965)Solar Distillation of
Water from Soil and Plant Materials: A Simple Desert Survival
Technique.Science 149(3690)1377-1378
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