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How To Build A Solar-Powered Still To Purify Drinking Water

solar still

The author’s solar still, with one pan in it. The still actually has room for two of these. Note that the glass top is at an angle, allowing the water to flow down to the catch tube.

Everyone agrees that water is needed for survival and articles abound for how to find water and purify it for drinking. But all those articles have one thing in common: They are talking about purifying water from biological hazards.

Normally, the biggest hazards we face from drinking water are microorganisms: bacteria, protozoa and other parasites which can enter our system and make us quite sick. These are a legitimate concern and one that every survivalist must take into account. A case of dysentery can kill you, especially if you are already weakened or injured.

While those biological hazards are important, they aren’t the only thing we can find in our drinking water. Chemicals, radiation, salt and minerals can all be there as well. While a fine-enough filter can get rid of biological hazards, particulate minerals and radiation, it can’t do a thing about salt or chemicals. Activated charcoal will help some with some types of chemicals, but the only sure way to get rid of those is through distillation.

Distillation is a simple process, although it can be difficult to accomplish in quantity. It consists of heating the water to the point where it evaporates quickly or steam forms. Then, that water vapor is captured and cooled, allowing it to condense back to water.

The really great thing about distillation is that nothing else evaporates with the water. The only chemicals that could evaporate with it are those that have a lower vapor point than water does. There aren’t too many chemicals normally found in a liquid state at typical ambient temperatures, which also have a lower vapor point than water does. Alcohol is one of the few.

The problem with distillation is that it is a slow process, which means that heat has to be applied to the water for a long time, so that it can evaporate and be captured. In a crisis situation, fuel might be scarce, making the process of distilling water rather expensive, from a resources point of view. This can be solved by harnessing the power of the sun in a solar still.

When most people talk about a solar still, they are talking about a covered hole in the ground, which is used to purify water in an emergency situation, typically in a desert or other arid place. That’s not what I’m talking about here. I’m talking about building a permanent solar still, which can be used to distill water on a constant basis.

A solar still, like many solar collector devices, consists of a glass-covered box, which is painted on the inside. A pan of water is placed inside and the device is placed in the sun. Sunlight enters the box and heats the water, promoting evaporation. When the water vapor hits the glass, it condenses on it, running down the glass to a catch tube.

Directions to Make the Solar Still

To make a solar still of this type, you’ll need to make a box out of plywood. You can’t see it well in the picture, but the white line at the back of the still is a door, which flips down to allow the water pans to be placed inside it. For water pans, I used two large rectangular Pyrex dishes. To accommodate them, the inside dimensions of the box are 19 inches wide by 23 inches long. I was careful about this measurement, as glass commonly comes in pieces that are 24, 36 and 48 inches. Had I made the box just a little bit bigger, I would have needed to buy a 36-inch piece of glass and waste most of it.

Ultra Efficient Water Filter Fits In Your Pocket!

The front of the box (the end with the catch tube) is 6 inches tall, while the back of the box is 9-1/2 inches tall. This allows sufficient slope to cause the condensed water to run down to the catch tube (more on that in a moment). The sides of the box are constructed of two layers of half-inch plywood, while the bottom is of 3/4-inch plywood. That gave me sufficient thickness at the bottom to make it easy to connect it together.

The sides and ends of the box are double thickness, providing a notch at the top for the glass “collector” to mount into. The outer piece of plywood should stick up half an inch above the inner one. I purposely made the outer piece of plywood “short” so that it would provide a ready handle for carrying and moving the solar still.

When inserting the glass, it should be held in place by silicone caulk. Quarter round or base shoe can be placed above it to finish off the box. Be careful when nailing the quarter round in place, so as to not hit the glass with the nail or hammer.

A piece of three-fourths or one-inch thick aluminized insulated sheathing needs to be cut to fit the inside of the box and placed in the bottom, aluminum side up. The aluminum surface of this piece of sheathing and the entire inside of the box should be painted flat black to absorb as much light as possible, converting it to heat. The aluminum coating on the sheathing will readily absorb and transfer this heat to the Pyrex baking dishes. Pyrex is used to reduce the risk of breakage.

diagram solar still

The hardest and most important part of the design is the drip edge and catch tube. I used a rubber door seal (without the metal backer) as the drip edge. You can glue it in place with silicone caulk, allowing the caulk to dry fully before turning the glass over. Be sure to fill the “uphill” side, where the drip edge attaches to the glass, to provide a smooth transition for the water drops to flow down. The drip edge needs to be located directly above the center of the catch tube. So, you will need to place the glass on the box, mark it for the drip edge and then remove it to install the drip edge to the glass, before installing the glass into the solar still.

The catch tube is a piece of half-inch PVC pipe. The outside diameter of half-inch schedule 40 PVC is slightly less than seven-eighths of an inch, making it easy to put a hole through the side of the still for it with a spade bit or forstner bit. Drill partially through the opposite wall of the still’s box from the inside, so that there is a pocket for the catch tube to sit into. Glue it into this partial hole with silicone caulk to both seal the wood and hold the drip tube in place.

catch tube solar still

To make the catch tube, make two lengthwise cuts in a piece of half-inch PVC pipe, about 120 degrees apart. It is easier to do this if you make the cuts too long, and then cut the tube to length. The cut-out portion of the tube should span the entire still, with the full tube starting where it goes through the side of the box.

The drip tube should be held in place by a pin at the outlet end. This can be a small nail. Just drill a hole down through the side of the still’s box and insert the pin to keep the tube from pulling out. A half-inch slip to half-inch threaded coupler is attached to the end of the catch tube, with a barbed fitting connected to it. A short piece of tubing is connected to this fitting.

Using the Solar Still

The solar still can be used all day long, even if it is slightly overcast. If it is properly sealed with paint, it can be left out even in a rainstorm. To use it, place the still in a place where it will receive good sunlight, without any possibility of it being shaded. Point it toward the south so that it can capture the most sunlight. Place a water jug or food-grade five-gallon bucket so that the drip tube will empty into the bucket or jug.

Fill both Pyrex pans with water and place them inside the still, ensuring that the door closes securely, without any air gaps. While the solar still is not fully airtight, you don’t want the water vapor escaping into the atmosphere. Leave the solar still and come back later to collect your water.

You can use literally any water with a solar still. It does not need to be pre-filtered in any way. Debris left in the water will stay in the Pyrex pans, while the clean water will be distilled out. If the water used is dirty, full of debris and silt, you will want to rinse out the Pyrex pans when it is time to refill them.

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  1. Some closeups of the inside would be nice. I don’t quite understand how you have the drip edge and why it would be attached to the glass. I would like to build one of these for our cabin in the woods. We have rain barrels but not on site clean water source. This would be the ticket.

    • Without the drip edge on the glass, the water would riun down the inside of the box and aroung the catch tube.

    • You probably don’t want to drink distilled water. Its mineral content is close to zero (because no distillation process can avoid some solid particles being swept by water into the output, via physical processes such as tiny grains of solid salt being swept by air currents to the top of the distiller then washed out into the output). The small amounts of salt in drinking water are essential for your health. Drinking distilled water will quickly flush out sodium, potassium, calcium, magnesium and other elements found only in trace amounts in the human body, but without which we cannot live.

      • I drink distilled water all the time, in fact, if you drank your local city tap water, you would have many health issues.

      • There is nothing wrong with drinking distilled water. Ships generate distilled water when at sea. We get plenty of salt/potassium and other minerals from food.

        I would like to build a small fresnel lens water distiller. The lenses are cheap. It would be nice to be able to hook it up to some water supply that supplies water as it is boiled.

    • Rain water is amongst the cleanest you can get. Here in Australia, many drink it straight from the tank, no filters, no boiling.. Just straight, fresh rain water. Ive just spent the last year drinking rain water.. Did no harm!

  2. This looks rather dangerous with the high powered lens. Waterwise makes a small stainless steel distiller which is the size of a large pot and which is non electric. A small wood fire (or any heat source) gives you
    distilled water.

    • The Fresnel Lens he is using is extremely powerful as shown. Not sure if the colored glass was required or a weak link. I will experiment with small less efficient lens when they arrive. The experiment is another good indication of a smokeless/flameless distillation technique. Since my colloidal silver generator requires distilled water, might be my go to method for distillation.

      • A dark material is needed to absorb the sun. With a clear bottle, most of the sun light would simply go through the bottle and water. I’ve seen this demonstrated by passing the light through a water filled aquarium and burning wood on the other side

    • Dangerous? No more dangerous than a fire!

  3. silicone can’t be used for aquariums because it is toxic to fish so i’m thinking there might be a safer sealant for humans too. that’s the only improvement I can think of.

    • I’ve used my aquarium for years with silicone seal….fish did not die from it…

      • Though I don’t do fish, except for dinner, it was my understanding that silicone sealant was safely used with aquariums, thought I had also seen it on the TV series. Might require one that does not have dangerous additives? Your fish/pet store should carry SAFE products.

  4. I don’t know how I would make the cuts in the pvc. A router table perhaps ?

  5. Is it possible to use double pane glass for these projects ? How about glass from skylights ?

    • Insulated glass would hider the process as the airspace in double pane glass is the insulator which slows the transfer fo heat. Skylights often have a partially-reflective coating on the glass.

  6. I ordered a Solar book that had this solar still plan in it. I built it to specifications but even in 100 degree weather, it would only produce about a cup of water a day. This isn’t enough to keep even one person alive in a crisis. Anyone else build one of these stills? I thought about adding metal wings to it to reflect more heat. I wonder if this would set the wood on fire?

  7. OMG!! Rich! You furnished the information WITHOUT my having to order a book or to watch a video!!
    OMG!! I love you, Rich. You made my life 100 times easier today. Thank you! Thank you!! Thank you!!!

  8. I’m thinking your article should be amended to make it clear that only labeled “food grade” sealant should be used and NOT run of the mill regular silicone or caulks. If the choice is death by waterborne pathogen or potential slow debilitating illness from sealant, I guess use what you have, but if the idea is prepping now while resources are available, why use inferior and harmful materials?

    • well one person who understands that MOST silicones are indeed lethal..and that food grade silicones are the only kind you should consider using.. AND only after they have sufficiently cured (dried).otherwise you will poison yourself slowly.. a rapidly dwindling source of free fresnel lenses is big screen projector TV lens. people have been putting these TV curbside with the advent of flat screens ..and the lenses that are in the three color projection tubes also can be used as pocket sized fire starters. good luck folks…I got a feeling we may be needing these soon enuff.

  9. Going by the video as opposed to the article;

    This looks like a potential idea for all those people who saved their old DISH or DirecTV satellite dishes when they changed providers. I’ve read where covering the inner part of the satellite dish with “mirror tape” will focus sunlight onto the end of the dish arm and get things quite hot in short order when it is aimed at the sun properly. Stirling engine plans caused me to save my old DirecTV dish when we got cable out here in my neighborhood, and ditto with a much larger old DirecWay internet dish (DirecWay has since renamed to as well. They sit in the garage waiting for me to mirrorize them for solar power projects, some day. For a hobbyist with a metalworking lathe, milling machine and some determination, a Stirling engine could power a small generator, as has been done and documented online quite a bit. But in my geographical area, solar power is too often blocked by clouds/weather and the need to mechanically track the sun to keep the dish aligned. On the other hand, I’d bet even the small satellite dish could be boiling / distilling water fairly rapidly for emergency use, and much simpler to put together…

    • John Z…this is a great idea since I have 3 satellite dishes. Could you send me directions on how to construct for solar water still? I would greatly appreciate it. I’m a disabled senior, so very simple directions by the #’s would be very very helpful to me. I reside in HOT Arizona desert, so sun is not problemo. Thanks so much, and I will be looking for your reply. To your health & survival off the grid!
      Cynthia R

  10. Be aware that only drinking distilled water for a long time will result in mineral deficiencies if there isn’t an adequate diet. Certainly, in a survival situation, clean water is preferred over contaminated, but thought it worth mentioning. Great article!

    • Dangers of mineral deficiencies in distilled water is a long held myth. Think about it – the mineral content of water is a fraction of the minerals in the food we consume daily. The only way we would be deficient in minerals from drinking distilled water is if we fast for days.

    • Distilled water is pure water. Yes it is devoid of minerals.. but the minerals it is devoid of are inorganic minerals. Inorganic minerals are not only not beneficial to animals and people; they are actually detrimental to good health. Inorganice minerals are however drawn in by plants, trees, and veggies. Through the process of photosynthesis, the vegetable plants turn the inorganic minerals into organic minerals that ARE beneficial to animals and people. Distilled water is perfect water for you, me, and our animals to drink. No one dies from drinking chlorineless, fluorideless, mudless water.

    • All of you distilled water “experts” need to stop spreading your myths and lies. Distilled water is perfectly safe even long term.

  11. I am curious in a warm moist environment such as inside your still won’t bacteria thrive on the glass thus contaminating the water just saying …

    • The temperature inside the box will probably prevent bacteria from growing…not sure though.

      • First, let the water sit in the open so VOC has a chance to evaporate.
        Then distill the water to remove remaining contaminates/ chemicals.
        Store distilled water in bottles.
        If bacteria/ mold is a concern, pasteurize water with the parabolic dish or sun oven.
        Add salt/ citrus juice to water for electrolyte before consumption.
        That is my setup. Water source is rain barrels from shingle roof

  12. This would be a much better article if I could print it off. After all if we need a solar water distiller, we surely are not going to have power to access the internet.

  13. Can u post the schematic drawings plzzzzzxx

  14. Some additional thoughts:
    – Use coke cans painted black and seasoned outside the distiller to off VOC’s (Volatile Organic Compounds) then install them in rows below the glass from side to side to increase heat.

    – Use only pyrex glass cake “pans” instead of aluminum cake pans to avoid contamination. They are also very easy to clean.

    – Do not use Rubber or Plastic inside the distiller instead use a drip edge of 1/4 x 1/4 inch steel bar from hardware store – fasten it to the underside of the single pane glass using JB Weld which will adhere to glass and metel

    – Do not use PVC for catch tube, instead use 1″ copper M grade. A trough 1/3 the diameter of the pipe and desired length can be cut at a machine shop for cheap. Plastic will give off bad chemicals (VOC’s) with the heat of the inside of the box.

    – Extend the catch tube outside the box using a 1″ to 1/2″ reducer and enough 1/2″ copper tubing to enter your glass container. Use open jar with no lid inside of a foam ice chest to minimize evaporation inside the jar.

    Your design using the removable lid instead of hinges is a very good idea….no rusted hinges.

    – I would suggest at least double the size (enough room for 4 pyrex cake “pans”) for greater production. Much larger than that will make the lid too heavy to easily lift off for servicing.

    – I would use a shaded copper coil between the box and collection jar to cool the water and steam coming from the box or else steam will just exit the box through the drain tube back into the atmosphere.

    • When using the 1″ copper tubing make sure you do not cut off one side (length wise) or it.Lift it and straighten it. that way you can use it as the drip edge. You should be able to cut pass have its width to have a longer drip edge.

  15. Nice thought, would love a bit more detail. I don’t think drawing or picture give a very clear on where in the box you are putting this drip edge thing. Would love to make this, can you please improve the instructions? Thx

  16. Marge,search youtube with key words for what you want a video in”solar still’..or water purification w/o power…etc etc…you can find a video with detailed instructions on just about anything you want to do…and I mean anything…its amazing what you can find there…good luck everybody…we’re gonna need it!!!!

  17. Fun little project, but long term I see a problem with keeping the equipment sterile

  18. Why not use a stainless steel pan inside with a small float valve to maintain the water level on the inside and a large container on the outside to gravity flow and keep your pan full?

  19. They make solar stills. I’m making one for a science project. I think people sell them

  20. I run a charity organization and I need to know personally as how can you advice for big project in poor villages and famine stricken areas. Please give your skype, whatsapp or direct cell numbers so that I could talk to this experiment maker or any who you know is behind this experiment in youtube.

  21. Distilled water is okay in a pinch, but it is acidic and NOT good for the body long term. There are ways to make it alkaline.
    Add 1/2 tablespoon of baking soda to the gallon of water. It is best to use food grade baking soda, also known as sodium bicarbonate. If blood pressure is an issue, food grade potassium bicarbonate offers a viable substitute. Food grade potassium bicarbonate is available at wine making stores and web sites.

    Stir or shake the container to dissolve the baking soda. After mixing is complete, test the water to see if it is alkaline. If the water still tests acidic, add an additional 1/2 tablespoon of baking soda and repeat the process of dissolving the baking soda in the water. Test the water again to make sure it is alkaline. If the water still tests acidic after adding baking soda two or three times, a healthier source of water is necessary.

    • Just ran across the comments here.

      As for the water being acidic, distilled water is really perfectly neutral. (Distilled water is a 7.0) It is however slightly more acidic than the pH that is found in your blood stream. (Blood is 7.35 to 7.45)

      This has become a hot topic in health circles and there is a ton of claims that acidic blood effects your health. Simply put this is true, the easiest way to know if your blood has left the healthy range is to check to see if your in a coma. Outside of this range the enzymes in your cells stop working, leading to loss of consciousness and as you can imagine other severe issues.

      By putting bicarbonate in your water you are simply bringing the pH of your stomach acid closer to 7.0, which at best does nothing and at worse leaves your digestive tract open to pathogens that would normally have been killed off. It is true that a person with a really poor diet can face issues with blood acidity, but the other health issues associated with a poor diet will eclipse this issue. Your body has many natural buffering processes that keep your blood acidity at an ideal range, if you are really concerned a small magnesium supplement will do more to buffer your blood and is cheap, easy and won’t make your pure distilled water taste weird.

      As for taste, running your water through some stainless steel tubing will give it a light mineral flavor if you so desire. Give distilled water to your children, yourself and anyone else you love, there is nothing in well or public water that you cannot live perfectly healthy without. You will get the minerals you need from fruits and vegetables.

      I have been working on some designs for water distillation with the idea of marketing it to first world people and using the bottom line to fund 3rd world installations. I will try to email you Naumann Ansaari to see if these would be useful to you.

      • Hi Graves, were you able to finish work on water distillation designs? I am working with a village in Pakistan. The community lives next to a fresh water lake which has become toxic and polluted with chemicals and excess salt. The locals don’t have many options for drinking water other than the saline and chemical infused water from the lake. I came across solar still while looking at cheaper alternatives to reverse osmosis plant. Please let me know if you have any solution. Thanks

    • I just use food grade hydrogen peroxide . I also like to nun by distilled water through a carbon filter , makes great tasting water.

  22. Paul Bragg wrote many books on health, and each book has a chapter on the benefits of drinking distilled water. I believe my drinking purified water ( even from concentrated vegetable restored juices ) caused me great joint pain, which was totally cured by my switching to drinking distilled water. Pain was gone.

  23. I have a very important question for the Solar Powered Purifier.
    What is the minimum temperature need for it to Work Properly, and Efficiently.

    Thank You

  24. Like your design. I am planning a bit larger one and am thinking of using an aluminum water heater pan to hold the water inside. Seems like it would serve the purpose of heating and holding the water if I paint it black. Like to hear from anyone who has thoughts on that.

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