Solar Distillation    [Download a PDF Copy]
Using free sunlight, gravity, modern materials and imagination to
transform undrinkable saltwater into fresh distilled drinking water!


Punch Bowl Solar Distiller (saltwater)

In March, (2012) I began testing a new saltwater distillation tool made mostly
from clear polycarbonate plastic punch bowls.  I obtained most of my materials
from the local Party City.   For now, I call it the Punch Bowl Solar Distiller and
it's shown in Figure 1.  It is made completely from off-the-shelf components
with only a few minor modifications.  This tool may be useful in arid areas with
access to the sea and inland areas where the ground water has become salty or
similarly polluted.   This is my first practical solar distillation tool that is ready for
field testing and evaluation by others. 

Figure 2 shows the Water Globe - what I imagine is the ideal solar distiller. 
The punch bowl solar distiller presented here is as close as I've arrived to my
ideal.  My plan is to produce a 2nd generation tool that will be the Water Globe,
providing there is enough interest.


How it Works

The tool takes undrinkable saltwater and turns into fresh distilled drinking
water by controlling natural evaporation and condensation.  Evaporated
saltwater is pure water, free of salt and other impurities.  Water evaporates at
all temperatures, above freezing.  Heat will cause water to increase evaporation. 
Sunlight striking a black colored water vessel is a free way to heat water and
increase evaporation.  Having a clear enclosure allows sunlight to strike the
water vessel and conserves heat (greenhouse effect) causing more evaporation. 
Using this tool with natural sunlight, saltwater is heated inside the tool. The pure
water vapors condense on the (cooler) walls of the 10-quart bowls forming
water droplets that are drawn by gravity to slide down to the drain and into the
white bucket.  Water can be collected and stored for many days in the white
bucket.  A final SODIS or chlorine treatment is necessary before drinking water
that has been stored for many days.


How it's Made

Figure 3 shows all material components and tools used to make this solar
distillation tool.  All materials that contact water are food-safe.  The tool is
composed of rigid polycarbonate plastic including two 10-quart (16" dia) and
one 5-quart (12" dia) clear bowls, one 5-quart (12" dia) black (polyethylene)
bowl, one 2-gallon white bucket, one black (metal) enamel plate,  four bottle
caps, double back tape, and four small soft-grip binders clips to hold the bowls
together.  The only tools you need are a fireplace lighter and protective work
glove. The retail cost is less than $20 in materials.  One tool can be manually
assembled in a few minutes!


To Assemble this Tool, Follow these 7 Steps:

1.  Find a secure low traffic area to place the tool where it can get at least
     9-hours of direct sunlight.  The water filled tool is very wind resistant,
     so don't  worry about it blowing over.  It is designed to be left outside
     and working 24-7. 

2.  Select one of the 10-quart bowls to be the bottom and one to be the top.
     Carefully burn a 1-inch diameter drain hole through the center of the bottom
     bowl using a fireplace lighter (use protective glove).  Be certain to burn the
     hole from the inside out. 

3.  Place the bottom bowl on top of the white bucket.

4.  Add small feet to raise the 5-quart clear bowl.  I use bottle caps attached
     with double back tape for feet.  Other kinds of feet may be improvised. 

5.  Place the plate at the bottom of the black bowl.  The two components work
     as a heat sink.  Then place the black bowl inside the clear (rigid) 5-quart 
     bowl.  Tilt the rim of the black bowl forward about 15° in the general
     direction of the sun.  This will stabilize the two bowls and optimize
     exposure to sunlight.
      
6.   Fill the black bowl with saltwater and carefully place the assembly into
      the center of the tool.  Again, only the black bowl (and plate) hold
      untreated saltwater.

7.   Place the top 10-quart bowl over the bottom and secure the two bowls
      with evenly spaced small soft-grip binders clips. 


Every 3-4 days open the tool and check the saltwater level. Carefully add
more saltwater to keep the black bowl nearly filled. At the end of a week
(or two),  collect the fresh distilled water from the white bucket. Again, a final
SODIS or chlorine treatment is necessary before drinking water that has been
stored for many days.


The Results

Tests have been conducted under mostly sunny skies with temperatures ranging
75 ° -  82° F  (24° -  28° C).   So far,  the tool can produce 1-cup (250 ml) in a
24-hour period.  As is, this tool will produce about a gallon of fresh distilled
water from saltwater in about 2-weeks.  Hence, to be effective, many of these
little distillation tools are required.  Think of using these tools like a farmer who
plants his seeds, waits until harvest time, and reaps his reward. These little tools
are the seeds!

Also, I envision something like this tool as the basis for a larger distillation
assembly composed of multiple 'punch bowls' that feed distilled (fresh) water
into a central storage vessel.  Finally, I am considering using larger clear plastic
globes to make larger tools based on my punch bowl design.  I have located
suppliers to accomplish this.  However, some of these larger globes are priced
over $100.  Hence, cost may be an obstacle.  Again, Figure 2 shows the Water
Globe that I imagine is the ideal solar distiller.  A larger more perfect globe will
allow greater evaporation and improved accumulation and flow of condensed
water droplets.


You can follow this Solar Distillation Tool topic on the
Water|Sanitation|Hygiene forum.