Water may be boiled away, then condensed to form pure water as distillation. The water must be condensed high from the water source. This may be useful for desalinating water. Volatile substances in the water may evaporate along with this water. The builder and user are responsible for further research and for safety.
A glass bottle may be heated where it is curved outward, only if water is inside of it. Water's boiling point is 100°C, so the water temperature cannot get higher than this (unless it is superheated by reheating vapor with a secondary heat source). This takes heat away from the glass bottle, provided the heated air is allowed to escape around, not getting trapped in an air pocket outside of the bottle. If done properly, the glass bottle is prevented from overheating, which would break the glass. Once the water is boiled away, there will be nothing to keep the container just above 100°C, and the glass will break, creating a hazard. Safety is important to not get scalds, cause a fire or break glass. Then collect water vapor.
(stainless steel container; aluminum material is unfavorable)
Solar distillation or solar humidification-dehumidification method (HDH) is, as its name implies, useful for distilling water. A solar still and multiple effect humidifcation are two methods of solar distillation.
A solar still is a simple way of distilling water, using the heat of the sun to drive evaporation from humid soil, and ambient air to cool a condenser film. Two basic types of solar stills are box and pit stills. In a solar still, impure water is contained outside the collector, where it is evaporated by sunlight shining through clear plastic. The pure water vapour condenses on the cool inside plastic surface and drips down from the weighted low point, where it is collected and removed. The box type is more sophisticated. The basic principles of solar water distillation are simple yet effective, as distillation replicates the way nature makes rain. The sun's energy heats water to the point of evaporation. As the water evaporates, water vapor rises, condensing on the glass surface for collection. This process removes impurities such as salts and heavy metals as well as eliminates microbiological organisms. The end result is water cleaner than the purest rainwater.
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 can prove to be a useful survival skill and could provide an important means of obtaining 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 faeces, can be used inside the pit. If only the natural soil moisture is used, the pit must eventually 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.
Sea water still
In 1952 the US military developed a portable solar still for pilots stranded on the ocean which comprised an inflatable 24 inch plastic ball which floated on the ocean with a tube coming out the side. A separate plastic bag hangs from attachment points on the outer bag. Seawater is poured into the inner bag from an opening in the ball's neck. Fresh water was taken out by using the side tube which leads to bottom of the large inflatable ball. It was stated in magazine articles that on a good day 2.5 quarts of fresh water could be produced. On an overcast day, 1.5 quarts was produced. Similar sea water stills are included in some liferaft survival kits, though manual reverse osmosis desalinators have mostly replaced them.
The water vapor should be collected safely, and be mindful of volatile substances. Alcohol and certain volatile substances have a lower boiling point than water, so be careful that nothing poisonous also condenses into the end water supply.
- Anjaneyulu, L.; Kumar, E. Arun; Sankannavar, Ravi; Rao, K. Kesava (13 June 2012). "Defluoridation of Drinking Water and Rainwater Harvesting Using a Solar Still". Industrial & Engineering Chemistry Research 51 (23): 8040–8048. doi:10.1021/ie201692q. http://pubs.acs.org/doi/abs/10.1021/ie201692q.
- "Sea Water Still." Popular Mechanics, February 1952, p. 113.
- "Manual Reverse Osmosis Desalinator - NOTICE OF INTENT TO AWARD SOLE SOURCE, USAF". fbo.gov. 2012 [last update]. Retrieved July 3, 2012. Check date values in:
- Müller-Holst, Hendrik (2002). "Multiple Effect Humidification Dehumidification at ambient pressure: Optimisation and applications". Technical University of Munich. Retrieved June 6, 2008.
Solar still references
- US 3337418, "Pneumatic solar still"
- US 4235679, "High performance solar still"
- US 4966655, "Plastic covered solar still"
- Jackson RD, Van Bavel CH (1965 Sep 17). "Solar distillation of water from soil and plant materials: a simple desert survival technique". Science 149 (3690): 1377–9. doi:10.1126/science.149.3690.1377. PMID 5826532.
- Badran AA, Al-Hallaq AA, Salman IAE, Odat MZ (February 2005). "A solar still augmented with a flat-plate collector". Desalination 172 (3): 227–34. doi:10.1016/j.desal.2004.06.203. http://www.desline.com/articoli/5963.pdf.