Solar Stills May 13,2017

Sustenance ( Water )

Essential Water – Solar Stills and Transpiration


If you don’t have a well or access to surface water, you can still get water from moisture in plants and in the soil using a solar still.  This is a miniature example of the water cycle we see on Earth where surface water evaporates and then forms clouds and eventually condense into rain and falls back to the ground.  The wonderful thing about solar stills is that the water is pure and ready to drink.  On the negative side, it takes some time for the still to produce water so you may have to scale your efforts to match your requirements.  There are some kits available commercially but we are going to talk about fabrication in this article.

There are three basic configurations for solar stills: 

► Slopingo

► Concave

► Convex

You are probably most familiar with the concave design.  A hole is dug in the ground and cut vegetation or brackish water is placed in the hole.  A pan, bowl or other catch device is placed in the center (it is a smart idea to run a tube from the bowl to the top so you can access the purified water without having to take the still apart) and a clear plastic sheet is placed on top and anchored with spoil dug out of the hole.  A small weight (a rock will do) is placed in the center over the bowl to make the plastic slope down.  As sunlight shines through the plastic into the moist material in the hole, water evaporates and rises to make contact with the plastic sheet where it condenses and then slides down the slope to drip into the bowl.  Simple!





This works great if the soil is moist but you can’t hit the water table.  You can add moisture with your own waste water (including urine).  You could also add a hose to pour untreated water into the still (under the plastic but not into the bowl) to recharge the still without having to de-construct it.  Negative side – stored water is inside the still at a low point, the only way you can get it is through a sipping tube.



The concave device is similar but the clear top is a hard plastic cone or dome (although you could fabricate one with your plastic sheet by tying a knot in center and then securing that with a cord to a nearby tree).  The concave device requires a trough to run around the inside edge of the plastic cone so as water condenses it will slide down to the side of the device and into the trough where it can be routed to drain to a bottle.  Nice benefit of this system is you can elevate it and then place your catchment bottle below the device and take water as you need it. 



For a sloping device, you can use a box and lean the open top in the direction of the sun.  Again, add untreated water or moist materials into the bottom of the box and cover with a clear plastic material.  In this case, you need a catch trough along the bottom edge which drains to a bottle.  The diagram to the side shows evaporator trays but you just need some sort of material that the moisture can adhere to (increases the surface area and accelerates evaporation).  Like the concave device, you don’t have to de-construct it to get the purified water. 

While you may be restricted based on materials at hand, try to use materials that will not warp or degrade when they get wet and that do not leech chemicals into your now purified water.  Remember that plastics will break down in sunlight so be prepared to replace plastic as needed.  Solar stills are great ways to make use of waste water but you will have to experiment with them to see how much water you can get out of them.  You may need to adjust the size and number of devices to match up with your requirements.

Another method of capturing pure water is by transpiration.  Water is carried from the roots up to the leaves and then released by small pores in the leaves in the form of vapor.  You can place a bag over any non-poisonous plant and capture this water vapor as it condenses on the inside of the bag.  Select a leafy plant that receives a lot of sunshine (sunshine speeds up the process of transpiration).  Shake the branches vigorously to let insects or debris fall off.  Place a plastic bag over vegetation (a leafy tree branch) and seal it at the top of the bag.  Ensure that a portion of the bag hangs below where you tied it off as this is where the moisture will accumulate.  You may have to use several bags and tie off several branches to get enough water but as long as the tree stays green, it will continue to provide water (you have to drain the bags periodically so the water vapor does not get too high, but even if you forget, once you drain the bags transpiration will re-start). 

Transpiration bags are easy to fabricate and install with little expenditure of energy.  However, you will still have to experiment with the number of devices you need to get enough water for drinkin


► In the absence of other readily available sources of water, solar stills and transpiration bags are a viable alternative for finding water. 

► Solar stills and transpiration bags give you purified water, ready to drink.

► Solar stills are a great way to take used water that you might otherwise throw away and make it drinkable.

► Transpiration bags are easy to fabricate and install.


► Solar stills take some time and effort to construct.  Additionally, these are fixed devices, they are of limited use if you are on the move.

► Volume of water produced may be limited.   You have to determine the productivity of these devices and what mix you will need for your water requirements. 

► Next we are going to talk about water treatment and heating.



De Oppresso Liber 

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