The students designed a simple solar still using two plastic bottles and PVC piping to test the ability to desalinate saltwater through solar distillation. They tested both clean and dirty saltwater samples over two hours, monitoring temperature, water volume, and salinity. The still was not able to produce potable water within the testing time due to heat and water losses. Improvements like better insulation and sealing could increase efficiency and allow production of drinking water.

1. Solar Water Still for Saltwater Purification
Casey Ballard, Alex Kasko, John Thomas Lencke, David Traynham
BE 4120, Biosystems Engineering, Clemson University, Clemson, SC, 29631
Introduction
The two major ways to desalinate water are thermal desalination
and reverse osmosis. Most forms of thermal water desalination are
expensive due to the energy required to vaporize water. One
solution to this issue is using solar radiation. Solar water
purification is a simple, cost-efficient way of making clean
drinking water. This project was to demonstrate the efficiency of
creating a solar water still out of cheap parts often found around
the house. Both clean and dirty saltwater were used to determine if
the solar water still could successfully remove both salt and dirt.
Using two soda bottles and a PVC pipe, we were not able to
produce drinkable water from salt water in 2 hours.
Materials & Methods
• Two 2L Soda Bottles
• 14 in by ½ in Diameter PVC Pipe
• PVC Cement
• Drill & Drill Bits
• HOBO & HOBOware
• Two Different Water Samples
• Graduated Cylinder
• Refractometer
• Spectrophotometer & Cuvettes
• Infrared Gun
Two empty 2 L soda bottles were used, and the soda caps were
trimmed to the diameter of the PVC pipe at 0.75 in. The caps and pipe
were fused together using PVC cement to create an insulated seal.
Once dried, a hole was drilled to allow the HOBO temperature probe
to monitor the water for two hours. Two runs were done with two
water samples using clean salt water and dirty salt water. Over the
course of two hours the water level was monitored, and the HOBO
took temperature readings every minute. The water volume was taken
at the end to view the total evaporation. Salinity was measured of both
the original and distilled sample using the refractometer. Absorbance
readings were also taken for each sample. Finally, calculations were
developed for the evaporation rates and modeling.
Mathematical Modeling
Conclusion
The solar water still was not able to produce potable water after
two hours. Performing more runs of the same water could be used
to reduce the concentration of salt in the distillate and build up
more water with less salt. The brackish water also had more
solids in it, reducing distillation efficiency. A more efficient still
would also help to create more distilled water at the top of the
system. Insulation rated for higher heats would be better because
the bottle reached a hot enough temperature to denature the PVC
glue, causing water and heat loss. Having the pipe flush to the
bottom cap of the system would also increase water gathering in
the top bottle because it increases the area of the evaporated
water.
References
Drapcho, Caye. BE 4120, Unpublishedlecturenotes. Clemson University, 2022.
Gleick, P. (2008,July 23). Why don't we get our drinking water from the ocean by taking the salt out of
seawater? Scientific American. Retrieved April 25, 2022, from
https://www.scientificamerican.com/article/why-dont-we-get- our-drinking-water-from-the-ocean
Kumar, A. (2008, February 7). How to make | SolarWater Purifier / DistillationSyster with PlasticBottles.
YouTube. Retrieved April 25, 2022, from https://www.youtube.com/watch?v=KkLMk2HVqEc
Acknowledgements: We would like to thank Dr. Drapcho for her help throughout this project
and for providing the necessary information.
Results
Figure 1: HOBO Graph of Clean Saltwater Figure 2: HOBO Graph of Dirty Saltwater
Measurement Clean Salt Water Dirty Salt Water
Original Brix 4.0 4.5
Original Salinity (ppt) 31.5 35.5
Distillate Brix 0.5 3.0
Distillate Salinity (ppt) 4 23.7
Initial Volume 500 mL 500 mL
Final Volume 473.5 mL 490 mL
Table 1: Results of the two distillations, clean and dirty salt water
The temperature of our first run varied over time leading to a sporadically
increasing curve. This was due to inconsistent cloud cover while our second
run was much more consistent due to almost no cloud cover. The seal between
our two caps and the PVC pipe was not ideal which led us to lose distillate
from our top chamber. This would be remedied in future studies. Due to this
loss, not enough sample could be extracted for our absorbance readings but
especially in our dirty saltwater study the sample was visibly clearer. We were
still able extract samples for our refractometer measurements.