How to Make a Solar Still: The Ultimate Purification Device

A solar still uses sunlight to evaporate contaminated water and condense it into drinkable form — no power, no filter cartridges, no moving parts. The same principle the water cycle uses to produce rain, scaled down to a device you can build with a plastic sheet and a shovel, or carry folded in a backpack.

There are high-tech purification methods, such as desalination and reverse osmosis, but these methods are geographically limited and not portable. A solar still works anywhere the sun shines.

For a more advanced off-grid option, a solar-powered water purifier can treat larger volumes reliably in remote locations using UV light without chemicals.

The short answer: For a survival situation on land, a ground still built over a dug pit pulls water from soil moisture and produces roughly 0.25–1 liter per day. For sea travel or a packable emergency option, the Aquamate inflatable solar still produces 0.5–2 liters per day, floats on the water's surface, and needs nothing from the surrounding environment. This article covers how both work, how to build the ground version step by step, and a full review of the Aquamate.

Materials Needed

• A container – anything with a large enough opening to catch falling droplets of water (a cup, an empty plastic bottle, or a small cooking pot, to name a few)
  
  
• Stones or rocks
  
  
• A 6 x 6-foot sheet of clear plastic
  
  
• Loose vegetation (leaves from plants, if available)
  
  
• A plastic tube, a shovel, and tape are optional.

The Steps for Construction:

1. Dig a pit that is about 4 feet wide and 3 feet deep
   
   
2. Dig another small hole in the center of the pit and place the water container.
   
   
3. If using a plastic tube, run the tubing from the container to the outside of the pit. Tape can be used to secure the tube inside the container.
   
   
4. If loose vegetation is available, place the leaves inside the pit but do not obstruct the container. This will add moisture to the distillation process.
   
   
5. Cover the pit with the plastic sheet, but don’t let it touch the bottom of the pit. Anchor the corners with rocks to prevent them from flying off.
   
   
6. Place a small rock in the center of the sheet, just above the water container. Push down the weight gently until the sides slope to an angle of 45^o
   
   
7. Secure the edges of the plastic sheet with rocks and dirt to prevent the escape of moisture.
   
   
8. Close the tubing end with a knot or tie it closed if used.
   
   
9. Wait 24-48 hours. Do not open the plastic sheet, or the moisture will escape.

Wait Time and Efficiency

This type of solar still without vegetation can produce anywhere from a few hundred milliliters to 1 Liter of water in 24 hours, depending on the weather, the soil's moisture, and the still's size. Adding vegetation and creating a larger still can increase the amount.

A solar still is an artificial water purifier that imitates the natural mechanism used by nature to purify water. Like the natural hydrological cycle, the sun drives the process of purification. Solar stills distill water using energy from the sun.

The sun evaporates dirty water, which is then cooled and collected in pure form. It does not use fossil fuels as a form of energy. Unlike many artificial methods of purifying water, solar stills use solar energy to purify water. The obtained purified water is potable – safe for drinking and cooking.

The main purpose of a solar still is to remove impurities from seawater or contaminated water by extracting pure water without using an external power source.

Stills leverage energy from the sun as opposed to fossil fuels by retaining enough heat from sunlight to form pure water vapor. The pure water vapor is then collected and condensed to liquid form as it cools. The purified water can be used for drinking, washing clothes and utensils, bathing, cooking, and emergencies during water shortages and natural disasters without access to clean potable water.

A basic solar still typically consists of two water troughs – one water trough is filled with contaminated water, and the other is kept empty to collect purified water. A piece of glass is placed across the top of the contaminated water trough, angling directly down into the empty water trough. The bottom of the water trough filled with contaminated water is usually covered with black paint to help absorb solar energy from the sun.

Solar stills distill water using the two main scientific principles of the water cycle – evaporation and condensation.

Evaporation

This is the first main step of water distillation. It acts as a mechanism to separate pure water from the impurities. The dirty water is left to sit in the sun, allowing it to absorb solar energy. The water begins to heat up as the energy is absorbed. As the temperature rises, water is converted to steam – the purified water that needs to be collected. Solar stills assume that all impurities have higher boiling points than that of water, so certain contaminated water with impurities having a lower boiling point than water is not suitable. The generated steam then moves towards the glass ceiling, leaving behind the impurities in the water trough.

Condensation

This is the second main step of the distillation process. Once the evaporated seam hits the glass ceiling, it condenses as it loses energy in heat—the condensed steam results in pure water droplets. The water droplets flow to the empty water trough due to gravity as the glass ceiling angles downwards. The purified water collected in the empty trough is free from minerals, bacteria, and other substances that cannot evaporate with the pure water. Read our full article on water distillers for home use.

There are two main different types of solar stills:

Single Basin Solar Still

This type of solar still holds the dirty water in only one basin and has only one freshwater outlet. The shape of the cover may vary as there are different types of single basin solar stills – concave (concave wick solar still), hemispherical (hemispherical solar still), pyramid (triangular pyramid solar still), spherical (spherical solar still). Solar stills may also be integrated with an electric or solar heater (solar still integrated with heater) to help increase the basin water temperature.

Multi-basin Solar Still

This type of solar still consist of more than one basin holding the dirty water to be purified. The additional basins are made of glass to allow solar radiation to reach the lower basins. The number of basins may vary – two (double basin solar still) and three (triple basin solar still). The shape of the cover of the topmost basin may also differ – pyramid (triple basin pyramid solar still), flat, and angled (single slope double basin solar still).

Solar stills have a narrow use case, but within it they're effective. Key advantages:

• No power required. The only energy source is sunlight. A solar still works in a desert, on open ocean, or anywhere with direct sun — no electricity, no fuel, no consumables.
• Removes a broad range of contaminants. The process relies on evaporation, so anything that doesn't evaporate stays behind: salts, heavy metals, bacteria, and dissolved minerals. The collected distillate is chemically similar to rainwater.
• Output range: 0.25–2 liters per day. A ground still yields roughly 0.25–1 liter per 24 hours depending on soil moisture, pit size, and sunlight. A manufactured inflatable still like the Aquamate produces 0.5–2 liters per day under good conditions.
• Low cost and no maintenance. A DIY ground still requires only a plastic sheet, a container, and something to dig with. A purpose-built inflatable still is reusable with no filter replacements.

The main limitation is output. One to two liters per day is enough to prevent acute dehydration for one person, but not enough for comfortable hydration or cooking. In a survival situation that's often sufficient — for everyday home use, it isn't. Read our full article on portable water filters for survival and the outdoors.

While it is handy to know how to make a solar still if you're ever in a tight situation, nothing beats a professionally manufactured still designed to produce the most amount of water possible.

This inflatable Aquamate solar still is a great choice for emergency water purification. It provides an inexpensive way to extract pure water from seawater and contaminated water, including urine. Solar energy from the sun is used as a heat source, so no power is required. A solar still typically consists of several components, but this solar still takes away the hassle of placing all the required components together.

Inflate the still by mouth, fill its reservoir with seawater or contaminated water, then let the sun take care of the rest.

How it Works

Because the Aquamate solar still is inflatable, it can be easily stored and transported in a backpack or suitcase when traveling. When the base of the solar still is filled with impure water such as seawater, unfiltered lake or river water, or even damp leaves and brush, the heat from the sun will cause the water to evaporate and condensate onto the inside of the dome. The condensation drips down and collects into the reservoir, producing clean, distilled water.

The distillation process is slow, producing 0.5 to 2 liters per day, and is highly dependent on the sunlight's strength and the contaminated water's condition. But the ability to turn dirty water into drinkable water in an emergency is invaluable.

Perhaps the ideal situation to have an Aquamate solar still in one's possession is if, God forbid, stranded at sea. The Aquamate can float on the ocean and be secured to the raft while the sun provides enough heat to turn seawater into drinkable water. As long as the Aquamate remains intact, it can produce up to 2 Liters a day, enough for one person to survive the dangers of dehydration.

Build a ground still if you're in a survival situation on land — it requires only materials you can scavenge (plastic sheet, shovel, a container), works anywhere with soil moisture, and costs nothing. The tradeoff is output: roughly 0.25–1 liter per 24 hours, barely enough for one person. In a serious emergency, build as large as practical and consider multiple stills.

Choose the Aquamate if you're preparing for open-water scenarios or want a packable emergency backup. It floats, ties to a life raft, produces 0.5–2 liters per day, and requires nothing from the surrounding environment. For ocean crossings or a well-stocked emergency kit, it's the more reliable tool.

For everyday home water purification, solar stills aren't the right fit — the output is too slow for daily use. See our guide to the best water filtration systems for home for alternatives that work at household scale.