Crew 24 Extracts Water From Soil!

Purpose: To extract water from moist or frozen soil.

Result: Water was successfully extracted from soil collected near the Hab.

Context: Finding available water on Mars, in some form, is a critical element of many Humans-to-Mars scenarios. Current speculation holds that water could be found in frozen soil form (or perhaps even in muddy slurry form) beneath the Martian surface. We had some messy mud to scrape off boots and ATVs yesterday, which stimulated the thought, what is the difference between frozen soil and mud, but a few degrees. We determined to find some leftover moist soil, and to try to extract the water it contains with an improvised still. We were fortunate that the temperature had dropped below freezing overnight, and there were frosted areas of frozen soil still existing in shaded areas at 9:00AM, and some drying, muddy patches also.

(Click Image for Detailed View)
Frosty soil	Soil collection
Dirt soup	Water from dirt

Equipment Used: soil collection containers, pressure cooker, plastic tubing, nylon angle fittings, collection bottles, hotplate, camera.

Method: We collected a 2lb coffee can full of moist soil at 33 deg F (net weight about 5 lbs) , and a 5 gal lidded metal pail of frosted frozen soil net weight estimated at 50 lbs. There is no scale of that capacity at the Hab, estimates were made by comparing with combinations of exercise weights that are here. The coffee can was closed with it's plastic lid and sealed with duct tape to prevent water loss inside the Hab, prior to distillation. The pail was closed with plastic film, held down with the lid, and sealed with duct tape around the outside.

Lacking proper lab equipment for distillation, we improvised with a pressure cooker, plastic tubing , and nylon angle fittings from the EVA water bladder system. The handle was removed from the cooker (leaving the safety relief valve in place.) The threaded fitting for the gauge was removed and polyethylene tubing that was just the right size inserted. The tube led through the air to a glass bottle, approx 3 feet away, at a lower level than the cooker. The coffee can full of soil was poured into the pressure cooker, and the cooker lid sealed. Heat was applied by hot plate at 10:35AM.

• 11:00 AM: the cold, dense mass of soil was heated enough to begin boiling (judged by noises within the cooker, we had no way of inserting a monitoring thermometer into the soil inside the cooker), and soon steam began to appear at the outlet tube.
• 11:20AM: moisture droplets were visible in the outlet tube near the lid of the cooker.
• 12:00 PM: water was dripping steadily from the tube. We discovered that a lot of steam was escaping around the tube where it left the lid of the cooker. We removed that tubing, and pressed a whittled-down, nylon angle tube fitting into the hole in the lid, and attached 4 feet of clear vinyl tubing. The drops began to fall more quickly. We could see there was still steam escaping around the safety release fitting, and around the seal for the lid itself, but there was a steady drip of water from the tubing. It was a low pressure system, the tubing vented to air, and steam warmed the first 3/4 of the tubing but the last section remained cool and hard, so we knew we were not losing steam, or running at an overpressure.
• 2:36 PM: 100 ml had been collected. The system was shut down to cool while crew engaged in other actvities; it was deemed safer to not leave it running totally unattended, eventually the soil would cook dry and the temperature would start to go up.
• 6:00 PM: the cooker had cooled earler; inspection revealed moist conditions in the cooker
• 8:00 PM: cooker was reheated.
• 9:00 PM: almost another 100 ml had collected. The water in the bottle had a definite chemical odor.

Analysis: The water in the soil reaches boiling temperature, and becomes water vapor. The vapor escapes through the fitting into the vinyl tube, where it cools and condenses on it's way down. Liquid water drips into the bottle. The chemical odor may be due to plasticizer extracted from the tubing as the vapor reforms as hot water as it first condenses. It could also result from organic chemicals in the soil that vaporize near the boiling temperature of water. Further testing will be necessary to investigate these hypotheses.

Conclusion: This was a proof-of-concept test, we were not concerned with specific yield / feedstock ratios, or even water purity. The result was at least 200 ml of water from 5lbs of moist soil. This result clearly demonstrates that water can be extracted from soil under the conditions we tested.

Future Study: Our next experiment with this equipment will be to extract water from the samples of frozen, frosted soil. The next steps beyond that require proper equipment to weigh samples, measure soil moisture content, monitor temperatures in process, and to distill through glass or stainless steel vessels and tubing. We would like to investigate ever dryer soils, and begin to determine yield ratios. Other approaches to heating the mass such as the microwave oven will be looked into. Future crews may be able to prepare equipment ahead of time to further these lines of investigation.