How to Make a Solar Still

Make your own distilled water and other liquids using these DIY solar still plans.

Solar Still

Turn undrinkable water into pure, crystal-clear distilled water with a home-built solar still.

Photo Courtesy Creative Publishing International

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With high energy costs and a warming planet that needs cleaner fuel sources, the time has never been better to get involved with solar energy. DIY Solar Projects (Creative Publishing International, 2011) by Eric Smith contains how-to instructions for many achievable, clever projects you can make and install in order to create your own solar lifestyle. Hundreds of people are doing it, and you can too. The following excerpt is taken from the chapter, “Solar Still.” 

You can purchase this book from the MOTHER EARTH NEWS store: DIY Solar Projects.

Make Your Own Distilled Water

Make your own distilled water from stream or lake water, salt water, or even brackish, dirty water, using these DIY Solar Still Plans. With just a few basic building materials, a sheet of glass and some sunshine, you can purify your own water at no cost and with minimal effort.

Distilled water is not just for drinking, and it’s always worth keeping a few gallons of it on hand. Clean water free of chemicals and minerals has a number of valuable uses:

• Always refill the lead-acid batteries used for solar energy systems or automobiles with distilled water

• Water delicate plants like orchids with distilled water; minerals and additives like fluoride or chlorine that are present in most tap water can harm plants

• Distilled water mixed with antifreeze is recommended for car radiators, as it’s less corrosive

• Steam irons become clogged with mineral deposits unless you use distilled water

The principle of using the sun’s heat to separate water from dissolved minerals has been understood for millennia, salt ponds being the best example of how this knowledge has been put to use in the past. In salt ponds, seawater is drained into shallow ponds and then baked and purified in the sun until all that remains are crystals of salt. In this case, the pure water that gradually evaporated away was considered a useless byproduct, but as far back as the time of the ancient Greeks it was known that seawater could be made fresh and drinkable by this process.

A solar still works like a salt evaporation pond, except that the water that invisibly evaporates is extracted from the air; the minerals and other impurities are left behind and discarded. As the hot, moisture-laden air rises up to the slanting sheet of relatively cool glass sealed to the box, water condenses out in the form of small droplets that cling to the glass. As these droplets get heavier, they roll down the glass to the collector tube at the bottom and then out to the jug.

The box is built from 3/4 " BC-grade plywood, painted black on the inside to absorb heat. We used a double layer of plywood on the sides to resist warping and to help insulate the box, with an insulated door at the back and a sheet of glass on top.

Finding a good lining or container to hold the water in the inside of the box as it heats and evaporates can be complicated. The combination of high heat and water containing salt or other contaminents can corrode metals faster than usual and cause plastic containers to break down or offgas, imparting an unpleasant taste to the distilled water. The best liners are glass or stainless steel, although you can also coat the inside of the box with two or three coats of black silicone caulk (look for an F.D.A.-listed type approved for use around food). Spread the caulk around the bottom and sides with a taping knife. After it dries and cures thoroughly, just pour water in—the silicone is impervious to the heat and water.

How to Make a Solar Still

We chose to paint the inside black and use two large glass baking pans to hold the water. Glass baking pans are a safe, inexpensive container for dirty or salty water, and they can easily be removed for cleaning. We used two 10 x 15" pans, which hold up to 8 quarts of water when full. To increase the capacity of the still, just increase the size of the wooden box and add more pans.

The operation of the distiller is simple. As the temperature inside the box rises, water in the pans heats up and evaporates, rising up to the angled glass, where it slowly runs down to the collector tube and then out to a container.

The runoff tube is made from 1" PEX tubing. Stainless steel can also be used. However, use caution with other materials—if in doubt, boil a piece of the material in tap water for 10 minutes, then taste the water after it cools to see if it added any flavor. If it did, don’t use it.

Turn undrinkable water into pure, crystal-clear distilled water with a home-built solar still.

View step-by-step photos of how to make a solar still in the Image Gallery as well as this PDF of the DIY Solar Still Plans

1. Mark and cut the plywood pieces according to the cutting list. Cut the angled end pieces with a circular saw or tablesaw set to a 9 degree angle.

2. Cut the insulation the same size as the plywood base, then screw both to the 2 x 4 supports with 2 1/2" screws.

3. Screw the first layer of front and side pieces to the base and to each other, then add the back piece. Predrill the screws with a countersink bit.

4. Glue and screw the remaining front and side pieces on, using clamps to hold them together as you predrill and screw. Use 1 1/4" screws to laminate the pieces together and 2" screws to join the corners.

5. Glue and screw the hinged door pieces together, aligning the bottom and side edges, then set the door in position and screw on the hinges. Add a pull or knob at the center.

6. Paint the inside of the box with black high-temperature paint. Cover the back and the door with reflective foil glued with contact cement. Let the paint dry for several days so that all the solvents evaporate off.

7. Apply weatherseal around the edges of the hinged door to make the door airtight.

8. Drill a hole for the PEX drain. The top of the PEX is 1/2" down from the top edge. Clamp a scrap piece to the inside so the drill bit doesn’t splinter the wood when it goes through.

9. Mark the first 19" of PEX, then cut it in half with a utility knife. Score it lightly at first to establish the cut lines.

10. Drill three 1/8" holes in the side of the PEX for screws, then insert the PEX through the hole. Butt it tight against the other side, then screw it in place, sloping it about 1/4".

11. Wipe a thick bead of silicone caulk along the top edge of the PEX to seal it against the plywood.

12. Shim the box level and tack a temporary stop to the top edge to make it easy to place the glass without smearing the caulk. Spread a generous bead of caulk on all the edges, then lay the glass in place. Tape it down around the edges with painter’s tape, then let it set up overnight.

This excerpt has been reprinted with permission from DIY Solar Projects, published by Creative Publishing International, 2011. 

11/26/2016 5:11:06 PM

Great read! Thanks for sharing. I love how detailed and clear the instructions are. I'd just like to highlight though that there are quite a few things that people should bear in mind when using solar distillers in general as there might be some benefits to it, there's also some downside to this device. My article on solar water distillation will explore more on that point. I'd love to share it to anyone interested in trying this one out. You can check it out here:

4/4/2016 8:37:28 PM

I was curious as to how much distilled water these devices can practically produce? Does anybody have any examples of how much their system produces how big the device was and where they live or how much sunlight they receive at their location?

10/27/2015 7:18:40 AM

Is this just for desalination? I feel really like a nube here--but I must ask: Does this purify the water from antigens, bacteria, viruses, or parasites? Or are these not specific problems with salt water? So, to be clear: With salt water, the only problem is too much salt, and the antigens, bacteria, viruses, and parasites are not a problem in this situation?

5/27/2015 4:37:50 AM

Knowing how to make something like this is great for people after a disaster like we are living here in Nepal. I'm OK in my home, but so many are living outside and it's starting Monsoon. I expect drinking water to become an issue soon, hence the interest here. Like everyone else in Nepal, I have a project..Hope the admin forgives me this one indiscretion.

10/3/2013 2:21:06 AM

I believe that people putting this story together just made an error. Mother Earth is good about correcting their mistakes. They're human just like us and they make mistakes too.

10/2/2013 7:27:59 AM

The article that came to me as an email said to make a' solar water heater', not a' solar water distiller'. That disturbes me. Say one thing and do another. Just another way to sell their books.

9/15/2013 11:32:25 PM

Caution with DI water, using it will result in electrolyte imbalance and mild to worse cerebral edema, aka brain swell. The gut can absorb 1 qt in 15 minutes of water. The salts are salts, these molecular structures are already so simple, there really is no such thing as organic salts. NaCl, table salt comes from a mine, the ocean or from your brow. It is an ionic bond, not a molecular bond and there can be pollutants in it. But it just isnt that hard to come up with clean salt. Its loss from our body leaving us Hyponatremic can leave us miserable on the path and really ill and an ICU patient on the extreme. Moderation is the key. I personally do not like the taste of DI water, never have even as a kid. Do not like over hard water either... Watch the wives tales, because it rhymes or has been passed along does not make it true. Other tales are gum collects in the gut, pepper collects in the gut, the colon becomes lined with whatever... RN, Nurse educator

ron thinnes
2/11/2013 2:33:41 AM

oops, leeching-leaching, momentary BF

ron thinnes
2/11/2013 2:31:57 AM

While it is true that distilled water leaches minerals out of the body it should also be noted that the minerals leached are "inorganic" minerals. Inorganic minerals are the result of water passing through soil where rock and whatever else is present. "Organic" minerals, however, come from plants and animals that eat the plants. ie, plant digests soil (converts it to organic minerals through photosynthesis, which only a plant can do), man and animal eats plants with converted minerals and on up the food chain. The inorganic minerals are sludge to the body because we do not do photosynthesis. It is good to get the inorganic minerals out of the body. Distilled water is a solvent and based at pH 7.0 (neutral) not acidic. Because most bottled water is placed in plastic containers the plastic components (chemicals) can leach into the water. That is bad. Distilled water is the same as rain. All life forms survive better with pure water which is "distilled" water. It has the ability to break the connection between organic and inorganic minerals and will then clean the body of impurities. I had a guy tell me that distilled water would kill house plants. I laughed my butt off. Give your house plants distilled water and they grow strong, healthy and very green. This is the effect of a solvent in a mineral base. FYI, the myth of distilled water leaching minerals came from a water filter company who was trying to build a market for themselves through filter sales. I have been drinking distilled water for many years and have NEVER had a problem with it. The body demands it. The digestive system becomes very regular when drinking it. Distilled water is excellent and that is what people have drunk for thousands of years. The reason for using a charcoal filter is to remove the taste from the steam process. It makes it easier to drink if you are just starting out. In this particular process the VOC's could be a problem. Put it to glass instead.

becky putzer
10/11/2012 5:55:48 PM

One major issue this article didn't adress is that distilled water is too pure for your body, because the water is acidic and demineralized, it will pull minerals out of your body when you drink it and it will pull contaminants out of whatever container you put it in. Also a distiller needs to have vents and a carbon filter to get rid of VOC's that build up from the distilling process. So #1. add vent holes and a carbon filter at the end of the tube before you bottle it in glass containers and #2 add about ¼ teaspoon of Himalayan salt per gallon of water to compensate for the minerals lost if you're using it for drinking.

mary whatley
10/5/2012 8:52:47 PM

Can someone tell me what the dimensions are once it's finished?

dave binderup
10/3/2012 6:42:18 PM

Great Idea! But just one caution: PEX may not be the best solution since it is not intended for exposure to sunlight (UV). Some brands do have UV inhibitors, but probably should not be used in continual exposure settings. In my opinion, copper is a better choice. UV isn't an issue with copper, it doesn't "off-gas" and distilled water has little to no minerals (copper's enemy and the reason for most PEX installations). The cost difference shouldn't be a big issue given the minimal amount used in this project. Cutting copper is more difficult, but still possible using a number of inexpensive tools including a rotary tool (ex. Dremel) or hacksaw.

10/3/2012 6:38:58 PM

Make sure the drinking bottle says PET not PC and you dont have to worry about BPA.

michael irvine
10/3/2012 4:35:30 PM

The plan overall sounds really good, but I wanted to point out a pretty major issue with the jug you show in the picture on the first page. The jug is 5-gallons, like the ones used for office drinking dispensers. Those however are made with BPA plastic and are among the worst of the leeching plastics. I can only imagine how much more placing the jug on your hot roof would speed up the poising of your "distilled water." A carboy could be a great alternative or I have 7.5 gallon totes I picked up from my local sporting goods store for water storage and they are BPA free. Thanks for the article, overall very good.

c zacarelli
10/3/2012 3:33:55 PM

Hey, great DIY! I think I am going to do this. Only make two of these, bigger and run the drain lines into my basement into two 5o gallon containers. this way I can water the gardens and incase of emergency, we will have 100 gallons of fresh, drinkable water on hand. Im also hoping I can find a small, Solar powered pump to push the water hard enough to spray from a hose or to even tap it into our water system for the house! Just need to find a couple LARGE tanks for the distillers...Hmmmm....