$8 Ziploc Emergency Solar Still
by louise-racette in Outside > Survival
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$8 Ziploc Emergency Solar Still





Solar Distillation seems like an obvious green energy win, right? Like - it's free energy. You can convert seawater to freshwater using just sunlight. Endless free water seems like it would be a really good thing. There are literally THOUSANDS of designs, some of them so simple that anyone can build them. So... why aren't people using solar distillation all the time?
After a deep dive into the existing types of Solar Stills (for like... way longer than a reasonable person would have done, this has been my special interest for a few years), there are 3 reasons that Solar Distillation isn't a practical solution for most situations:
- Cost - most Solar Stills are made out of glass/plexiglass, which is expensive to buy/store/ship
- Labor - many Solar Stills require a ton of construction effort or maintenance effort
- Efficiency - survivalist/DIY solar Stills just don't yield much water. Large-scale ones are better, but in most places it's cheaper to ship water than distill it.
Almost any type of Solar Still will yield at least some clean water, so I was specifically trying to figure out:
What's the cheapest Solar Still (in Dollars per Liter of Fresh Water) that people could actually use in an emergency?
This Ziploc Solar Still is a hybrid of the available options - cheap and easy to setup, but scaleable enough to actually be reliable in a disaster scenario. See "Variations" step for more detail on the existing Solar Still designs.
Pros:
- Cheaper than a permanent still or floating still
- Easier than digging a pit still
- Higher output than a small-scale/experimental still
Cons:
- Uses plastics (see the "second-stage filter" step for more detail)
- Has salty water physically above clean water (you have to be careful taking water out - see "prepare the salty water" step for detail)
Supplies





For each Ziploc Solar Still:
- 20-gallon Jumbo Ziploc (or equivalent brand) plastic bag. Clearer is better, thicker bags will last longer.
- 2x Aluminum Disposable Catering Pans (20.5" x 12.5" x 2.75" or similar). Any other plastic/cooking pan would work as well, these pans are cheap and light while also being strong enough to avoid spilling salty water.
- Scrap cloth (cotton or other natural fibers work best)
- A reflective emergency blanket
- A 2-liter soda bottle (or any bottle of similar size)
Other Supplies
- A hand balloon pump
- Food dye
- An outside area with as much sunlight exposure as possible
- A sunlight-tracking app (this can help with still placement/predicting where shadows will fall later in the day)
- A table or raised surface to put the Ziploc Solar Still on
- An off-the-shelf water filter (Brita or similar) - helps remove any microplastics left over from the Solar Still. See "second-stage filter" step for details
- (Optional) Clothespins/Binder Pins (can be useful to stop parts blowing away when it's windy - ask me how I know)
Some math:
- At 2025 prices (sourced from Amazon), each Ziploc Solar Still costs about $8.31 (not including scrap cloth or the "Other Supplies")
- The highest yield I've gotten from a single Ziploc Solar Still was 670 mL during a 24-hour period (in Portland, OR with midsummer direct sunlight during 100-degree weather)
- An adult needs somewhere between 2.7 - 3.7 Liters per day to survive - in an actual survival scenario you'd need a minimum of 6 Ziploc Solar Stills per adult
Gather All Supplies

Gather everything you'll need for the project
Cut Cloth to Fit Inside the Aluminum Pans


I've had much higher yields when using natural-fiber cloth as a wick inside the still than from just heating water directly - this has to do with capillary action vs bulk thermal absorption in water. Generally a darker natural fabric will work best - I used a scrap t-shirt for this DIY still. A wick that's partially out of the water will evaporate the most water vapor.
Place Emergency Blanket and Jumbo Ziploc


Be sure to wear sunglasses if you're doing this in bright sunlight! I've tried putting the emergency blanket inside the Solar Still, but found that it sheds bits of mylar into the clean water. Keeping the emergency blanket dry works a lot better.
Place Aluminum Pans and Soda Bottle Inside Jumbo Ziplocs


Place your Ziploc bag and pans outside in the location where you want the Solar Still setup - I recommend setting up all the materials dry, then adding water afterward. You want the 2-Liter soda bottle to stay upright.
Prepare the Salty Water

Because this Solar Still has salty water sitting physically above distilled water, I add food coloring to the salty water to make sure that any spills are easily-noticed. Add about 7 teaspoons of salt to tap water in order to approximate seawater.
Add Water to the Still


Pour water into the two pans while they are inside the Ziploc. I usually add about 1 Liter to each pan, you can experiment with more or less.
Inflate the Still and Seal Zipper Shut




Zip the bag most of the way shut, then use the balloon hand pump to inflate the Solar Still until the sides bulge out. Seal the Solar Still fully.
Wait


The sealed Solar Still may inflate/deflate slightly as air leaks out and the temperature changes. You should see condensation forming on the outside of the bag and running down the edges. If you're not seeing much condensation, check:
- Is there a wick? Is the wick partially exposed to the air?
- Is the bag inflated and sealed? If there are air gaps (even small ones) you will see a lot less condensation, especially near the air gap
- Is the Solar Still in direct sunlight?
The Solar Still will only evaporate significant amounts of water in direct sunlight - I usually wait until late evening to collect the day's water.
Carefully Open the Bag and Remove Pans


At the end of the day, wipe off any dust/debris from the Ziploc bag, carefully open the bag and remove the Aluminum Pans/Soda Bottle. It's very easy to spill water in this step (either the salty water in the pans or the distilled water below the pans). Be sure to set the pans down on a clean surface!
Pour Clean Water Out of the Bag

Pour the water into a collection container.
(Recommended) Run Desalinated Water Through a Second-Stage Filter
This Ziploc Solar Still uses plastics exposed to UV light and higher temperatures, which can leach BPA/microplastics/other chemicals into distilled water. While it may seem redundant to run water through two different types of filters, household Brita filters aren't able to remove salt/heavy metals from water (the individual ions are too small for an activated carbon filter to remove them). However, larger molecules (like microplastics) can be removed by a household filter. I haven't had the chance to test this formally (if someone reading this has access to a Gas Chromatograph I'd love to get some better test results!), but I've noticed that a household filter dramatically reduces the scent/taste of plastic from the distilled water.
Setup the Ziploc Solar Still for Another Day
You can use this Ziploc Solar Still repeatedly- however much distilled water you were able to get out of the still, add back that same quantity of salty water (for example, if the still yielded 600 mL you should add back 300 mL into each pan). Be sure to be careful with the bottom of the pans - these will be in contact with the clean water. You don't have to add more food dye, if everything is working the food dye will stay in the pans over repeated use. I haven't used one of these stills for longer than a week, over an extended period of time watch for holes/leaks/yellowing in the plastic.
Variations!


I've tried dozens of variations of this design and I'm curious to see what you come up with! Some of the fun things I've tried:
- Different wick designs
- Various fibers (synthetic vs. natural vs. paper)
- Different types of wicks - I've had the best luck with a "mini-clothesline" type, but that took a lot of work to make
- Carbon-coated blotter paper (based on this research)
- "Hammock" designs (so you don't need a table and can instead hang this from a clothesline)
- Different bag sizes
- Different materials (silicone, PVC, etc.) - just be careful with health/safety warnings for the material
Please post your ideas in the comments!
References - Other Types of Solar Stills
Desert-style "Pit" Solar Still
Pros:
- Portable
- Cheap
Cons:
- Requires a lot of creation/maintenance time (you have to dig a pit and fill it with plant matter)
- Inefficient (you don't get much water out, largely because the pit is not very well sealed no matter how much dirt you add)
- Risk of wildlife getting into the still (or someone falling in)
Navy-style "Floating" Solar Still
Pros:
- Efficient
- Portable
Cons:
- Very Expensive
- Does not work as well on land
Glass-style "Permanent" Solar Still
Pros:
- Efficient
- Safest for long-term use (materials hold up well to UV light)
Cons:
- Not Portable
- Expensive
Miscellaneous "Small Experiment" Solar Still Designs
Almost any design will work to produce some small amount of clean water, but few of these would realistically scale up to the amount of water needed for an adult.
Pros:
- Cheap
- Many are fast and easy
Cons:
- Doesn't provide much output water
- Can be hard to maintain