A friend of mine and I just finished teaching a 2-day Wilderness Survival course for a group of St. John Ambulance cadets, aged 11 to 16. Part of the course involved demonstrating various ways to collect water in the wild. <br><br>We had some success with a clear plastic garbage bag draped over a small deciduous bush, about 3 feet high. I tried to demonstrate a solar still using a green plastic garbage bag (slit down one side and along the bottom). I reasoned (never having made one before) that the green would absorb the sun's heat and increase evaporation from the soil underneath.<br><br>Part of the problem was that we didn't check it until almost noon the next day; I wanted to make sure that the cadets at least saw what it looked like before I took it apart. There was some condensation in the metal pan but nothing that I would call "drinking water". <br><br>Would clear plastic work better? Did I just wait too long?<br><br>None of the survival manuals I have says anything about what type of plastic to use. Two days after we returned, I was in Mountain Equipment Co-op and I saw a new survival blanket from Adventure Medical Kits. This one is 5' x 8' and is bright orange on one side; the orange side has survival and first aid tips/instructions printed on it, so it serves triple duty. The survival instructions say you can use it (the space blanket) to build a solar still, so it would appear that being transparent is not a requirement, although I would suspect you still need to build it with the orange (non-shiny) side up.<br><br>Any advice on what we did wrong? Does anyone have a list of common mistakes made when building a solar still?<br><br>On a related note - it seems to me that it would be fairly easy to build a simple distillation apparatus out of a cup and a Zip-lock bag. Fill the cup with contaminated or salt water, put a funnel over it upside-down, place the assembly inside the ziplock bag and seal it. The sun's heat should cause the water to evaporate, and the funnel would prevent it from going back into the cup when it condenses later. I haven't tried this yet; does it make sense?<br><br>Thanks in advance, btw; this stuff is fascinating.<br><br>

SolarStills- look at the name. We are hopefully collecting water available from the local environment. Sea Stills are wonderfull for distilling salt water- Lots of Ocean .Small transpiration bags secured to safe vegetation are also productive. The dedicated solar still is not. Do a simple experiment. Acquire one of the rather inaccurate moisture meters sold in nurseries. Dig your hole and wait. Has any water seeped in?If it has you could readily sop it up with cloth or sponge.Now stick the meter in. Where is the water? Down in the local water table. Ever try to drown a gopher? Soil is one big sponge! Solar stills rarely work, and if they do the water could have been easily gathered as seepage anyway.They have one good use. If some Crocodile Dundee instructor writes euphorically about solar stills they haven't really used one. Makes a good credibility reference! Using a skill assumes the worse scenario. If I can't do it in my backyard I surely won't try it in death Valley.<br><br>

LOL chris soon as i seen "Solar Still" and chris kavan. i new u where telling him it doesnt work! lol cause ive been through your "Solar still lecture" before !!!!<br><br>

I just tried your cup still. I used a Heat Lamp and a bottle of contact lens saline solution. It works more or less o.k. I haven't pursued it to a salt encrusted cup and Perrier in the Ziplock yet. The only obstacle is size. If you have the time to create a functioning still to treat a contaminated water source, you might just as well fashion a full sized one. I think I'd sweat a cup of body fluid at least just watching in anticipation! It would be a great training aid though.<br><br>

I agree with Chris, solar stills rarely work. Don't count on them in a life or death situation.<br><br>Ted Fisher<br>VCSAR<br><br>

We've already committed to running the course again next year, for the Air Cadets (and any St. John Ambulance cadets who didn't attend this year but still want the proficiency badge). I think I'll do as Chris suggests and use it (the Zip-lock, cup and upside-down funnel) as a training aid - it seems to me it's exactly the type of thing that kids that age will have fun doing. But I'll practice with it to see how well it works, first.<br><br>Chris, is your complaint with the solar still about the whole concept, or is it just the notion of water evaporating from the earth? In other words, do you think the solar still is effective as a means of purifying salt or contaminated water, or are there better ways of doing this?<br><br>

I'm not qualified to comment on the general usefulness of solar stills- I've never tried to use one, so I'll stay away from that issue (the East generally has more water than sunlight). I will just say that it was my impression that it was important to use clear plastic, in order to take advantage of the greenhouse effect- the idea is for the air and moisture inside the pit to heat, not the plastic itself, which after all is the condensing surface, so I would think the clearer the better. I was also under the impresson that part of the idea was to fill the pit with moisture-containing vegetation, bad water, urine, whatever is available- I never had the impression that much water was expected from the soil itself.<br><br>I do remember that in "The Complete Walker III" Colin Fletcher mentioned some plastic that was supposed to be better than most, and I remember seeing ads in Backpacker magazine for that plastic shortly after the edition came out. I can look it up if there's any interest.<br><br><br>

Solar stills are great as distilleries. but again look at the word. We are making the water potable. This assumes a SUPPLY of water to distill. As a device for collecting that water, they are woefull failures. Doug discusses their antecedents . It was a development for military survival. Trouble is, it was never really tested in the real world before being promoted.As I said, if somebody writes euphorically about the gallon of mountain spring water gathered while crossing the Sonora desert: they're either liars or ate peyote instead of prickly pear fruit by mistake.<br><br>

Addendum: None of us are infallible or have all the answers. A good instructor is the one who is also the best student. Hopefully a student returns and teaches us something they built on our knowledge. The bad instructor is the one who's lesson plan for English literature can be recited by your older brother and parents.I once listened to a talk by the Dalai lama. he quoted a scripture. A young monk said he had misquoted it. There were scowls from the senior monks as his holiness continued to lecture. Suddenly the Dalai lama broke into laughter." Oh,Oh, you were right, I was wrong!"<br><br>

The solar still was cooked up by two Department of Agriculture Scientists. So far, I've found clear, opaque and black listed in various references on constructing one! You must also factor in the 'sweat equity' in constructing one of these things. 'Dig a hole approx. 4' square by 3' deep' is the MINIMUM size I found.As an exercise dig one sometime. Don't drink any water either.Remember, this is a survival situation.If you succeed remember that a series of holes must be dug after the immediate water has been distilled from the first hole.Now try the plastic bag wrapped around living vegetation. As John Wiseman points out in his SAS book, The water may be 50' down. The tree is a natural waterpump.<br><br>