The key word here is CONDENSATION. I’m sure you have made yourself a glass of a cool drink of some type on a hot day, and the outside of the glass gets droplets of water on it. That’s condensation, and that’s the key to obtaining water from a solar still.
Making a solar still in a survival situation depends on three factors:
- Do you have ANY source for water?
- Do you have any vessel for collecting water?
- Do you have a piece of plastic, preferably clear?
- Is there SUN in the sky?
It’s actually hard to make a solar still in a cloudy region. Ironically, while you are stranded and in dire need of water, you need the brightest sun there is for the best results. Hot days often mean cool nights.
These weather conditions allow for another method of water collection that we can mention in less detail, a Dew Catcher or Overnight Collector, as the focus of this article is distilling water by means of a solar still. For either method, if you happen to have a piece of plastic, then you are half way there.
Mentioned in Passing: Overnight Collection
If you have that sheet of plastic that you intend to use for your solar still during the daylight hours, you can also put it to use collecting dew overnight or when the weather is not optimum for solar collecting. Especially in a wooded area during warm, or hot, weather.
Stake out the plastic sheet up off the ground a couple of feet. Leave some slack in the plastic. Take a small, clean stone and place it in the middle of the sheet to cause in to sag down in the middle, about a foot deep. Overnight condensation will form on the sheet of plastic, and roll down into the dip you made with the stone.
When you wake up in the morning, you will have a little water to drink. The amount of water you will collect depends on the humidity conditions. The water will collect on the top side of the plastic. If you have that vessel handy, it’s not a bad idea to put it under the plastic to catch water that may form on the underside.
Water will run down, and drip off the plastic into your collection vessel. If you have to use a piece of the plastic to collect the water, simply dig a small hole directly under the point of the plastic sheet. Place the smaller piece of plastic in the hole to catch the water drops.
While this is not a solar still, it works on the same principle of condensation. The difference is that with the solar still you are, in effect, forcing condensation to occur. Whereas, in this method, it is occurring naturally. The Overnight Collector collects dew, so it actually works when a solar distiller is not ideal, or the conditions are not ideal, for using the sun.
Back on Track
So let’s say, we have established that you happen to have a piece of plastic with you. You can use a small piece of the plastic to make a collection vessel if you have no other alternative. It won’t be ideal, but it will work. A cup, a can, or an empty bottle of some type would be a better vessel for collection. But you can make do with the plastic sheet.
If you have the mindset, you could make a wooden bowl or cup (but that’s another article). For the sake of this article, we will say that you have an empty water bottle that you happened to have had with you on your foray into the wild.
First and foremost, you need some kind of water. ANY kind of water, even sea water, will work. Actually pee will work, but you aren’t going to survive for long distilling your own pee (because you would get less and less each time). It doesn’t matter if the water is dirty, or muddy, it can even be still, stagnant water. It may retain a little dirty taste, but overall, it will be clean water once it has been distilled.
Once you have located your water source, you are ready to make your survival solar still. First, dig a hole a little smaller than your sheet of plastic. If you happen to have a very large sheet of plastic, you may have better results making a couple of smaller stills rather than one large one.
Survival Solar Still
- Dig the hole and set the removed dirt, or sand, near the hole as you will need it for a later step.
- Place your collection vessel in the center of the hole, and fix it firmly by packing some of the loose soil or sand around it.
- Next, pour your water in the hole. AROUND the collection vessel, but NOT in it. Make sure to pour gently, to make sure you don’t splash dirty water into your collection vessel.
- Cover the hole with the plastic, leaving it slightly slack.
- Cover the outer edges with the soil or sand from digging the hole. Place a dirt clump, or a little sand, or a small stone in the center of the plastic to cause it to dip down so that the point is directly above your collection vessel.
What happens now, is that the sun shining into the plastic creates the greenhouse effect and the temperature inside the hole rises. This causes water vapor to condensate onto the bottom of the plastic sheet. The water droplets will run down to the point made by placing a rock etc. on top of the plastic and subsequently drip into the collection vessel.
This water is free of contaminants and impurities and is fit for drinking. If you wish to take the extra precaution of boiling the water you can. Usually you don’t really get a lot from a solar still in this manner, so you might not want to risk wasting it by boiling it.
Solar Still at Home
You don’t have to be in a survival situation to want to make a solar still. Oftentimes the tap water that is supplied to your home has “acceptable levels” of chemicals, including lead, that you don’t want to drink. Using a water filter at the tap or a filter pitcher can remove a lot of these unwanted elements. But you can also distil the water to make it more pure.
Here’s a video of a DYI water still you can make at home:
DYI Solar still at home
- To make a solar still at home start by building a box (the size depends on how much water you wish to distil). The box should have a bottom half and top half, both halves should be sealed and air tight. You may hinge the top half to make it easier to access. The top half will be slanted at a decent angle, about 30 degrees, and it will have a glass cover.
- At the lower end of the lid you will make a collection tube that extends to the outside of the box with a hose to an external collection vessel. The hose should be of a food grade type or aquarium use rather than a garden hose as a garden hose will cause the water to have a plastic/vinyl/rubbery taste, and you don’t want that.
- The collection tube is made by cutting a piece of PVC pipe along the length. You don’t want to cut the pipe in half, but rather make two cuts that remove about 1/3 of the diameter of the pipe. Leave about 1” at one end and about 3” at the other end uncut.
- To install the collection pipe, drill an appropriate sized hole half way through one side from the inside. The hole should be positioned so that the collection pipe can be turned so that one edge touches the glass cover. Drill another hole all the way through the other side at the same position, the 1” end goes into the partially drilled hole and the 3” end extends out of the box through the other hole.
- Use silicone caulk to seal the hole, and to glue the pipe into place in the other hole. Do not let caulk be where it will come into contact with the water. Attach appropriate fittings to the end of the pipe that extends out of the box, and attach the collection hose to that.
If you wish to paint the box a dark color to help it retain heat, be sure to use a water based latex paint, and not oil based. To use the solar distiller, simply place shallow trays of water inside, and position the box so that it receives plenty of sunlight.
The evaporated water will condense on the underside of the glass, and then run down into the collection pipe, as the pipe fills the water will run out of the collection hose into your collection vessel. This water is pure and ready to drink (although it might be a little warm).
You may wish to collect the water and refrigerate it to have a cool drink of pure water later, or you can collect it into gallon jugs with tightly sealing lids and store it for your prepper stockpile of water.
Here’s a video of a survival solar still: