Drifting in an open sea creates one big dilemma: you are surrounded by seemingly endless water everywhere you look, but not even a single drop of it is drinkable. Human body can drink saltwater indeed, but seawater is an entirely different story. Seawater contains higher concentration of salt; when digested, your kidney has to work harder and uses any existing water in your body to get rid of the salt. Drinking seawater does not cure your thirst. It can kill you instead. Having good supply of freshwater onboard creates the difference between survival and slow death from dehydration. Now with an abundance of seemingly undrinkable water all around you, Katadyn 35 Survivor Desalinator comes to the rescue.

The idea is simple. Katadyn 35 Survivor Desalinator helps you transform an otherwise undrinkable seawater into perfectly healthy freshwater. As simple as it may sound, there is a lot of serious engineering going on inside this small equipment. It is compact hand-operated equipment that functions without electricity of any sort. All it takes is hand power to operate the pump. On the inside, the desalinator has a semi permeable membrane to filter out salinity and other impurities from seawater. The pump generates about 800 psi pressure to force seawater against the membrane. Harnessing the power of reverse osmosis mechanism, salt molecules and impurities will not be able to pass through the membranes, leaving only water molecules for you to drink.

Quick Facts about Katadyn 35 Survivor Desalinator

• The overall dimensions measures a mere 14 x 55.9 x 8.9 cm and it weighs 3.2 kg. It is compact enough to carry by hand or used as emergency kit on a boat.
• It provides maximum volume of 4.5 liters per hour with optimum pump frequency of 30 times a minute, making it effective to produce freshwater for 20 people a day in the middle of the sea.
• Salinity filtration reaches 98.4% on average, but it can filter out at least 96% of salt molecules from seawater. This is more than enough to produce drinkable water from the sea.
• Hand-operated desalinator.
• Built from stainless steel and plastic materials to be a heavy-duty durable equipment to withstand rough environment and treatment.
• Used by militaries worldwide, and the membrane has been approved by the U.S. Food and Drug Administration (FDA)
• Katadyn 35 Survivor is one of the prescribed pieces of equipment for Around-Alone sailing regatta.

Energy Recovery

The biggest downside of removing salts from seawater through reverse osmosis is that it requires an extremely high pressure of 55 bar (nearly 800 psi). Katadyn 35 Survivor only has manual pump because it is intended to be hand-operated equipment, and therefore it takes quite a lot of power. Assuming you need to produce 4.5 liters of drinkable water in an hour, you will have to pump the desalinator as many as 30 times a minute. This is physically-demanding equipment, but Katadyn comes out with smart solution.

Most seawater is wasted throughout the filtering process. This wasted water still stores the energy or pressures from the pump. Instead of simply discharging the energy, Katadyn 35 Survivor re-circulates the water to the back side of the piston to aid every next stroke you need to make. This energy is always contained in the mechanism, allowing you to do less work without reducing results.

Keep in mind that only 10% of the seawater inside the desalinator passes through the membrane and comes out as drinkable water. The remaining 90% simply moves away because it still contains high salinity. When it flows, the membrane is swept clean from impurities, creating a self-cleaning mechanism. An amount of 10% may not sound satisfying, but it is necessary to make sure that only drinkable water passes through the small membrane pores. The image below from Katadyn 35 Survivor documentation explains energy efficiency and self-cleaning.

Without the energy recovery control valve, every stroke requires the same amount of energy as the previous one. With Katadyn 35 Survivor, pumping action is a bit rigorous during the first few strokes. As the energy from wasted seawater builds up, the pump operation becomes less demanding. Another good thing is that the compact design only works your arm and back muscles; both of which are more sustainable and easily recovered during the pumping. The bigger portion of the equipment can be put down on a hard surface, meaning you can operate the pump using one-hand only. If you find it difficult to make it sit firmly on a raft, you can always put it across your lap.

The membranes can get dirty due to accumulation of particles or biological growth. Under this circumstance, flow rate of freshwater is possibly reduced and the pump becomes more difficult to operate. Katadyn also offers membrane cleaning kit in two variants including Alkaline Cleaner and Acid Cleaner. The former is effective to remove dirt or oil, while the latter is best for removing mineral buildup. In most cases, alkaline cleaner will solve all problems and restore membrane performance, but acid cleaner helps to optimize output. If cleaning no longer restores performance, it is a sign that the membrane needs replacement.

Certifications

• Approved as desalinator as defined in 1983 conditions of the Safety of Life at Sea Convention
• In the U.S., Katadyn 35 Survivor is approved for usage by United State Coast Guard and it fulfills Federal Aviation Requirement
• In Canada, the kit is used by Transport Canada Coast Guard and it complies with Air Navigation Order

Weight: 7 lbs - 4.5 liters per hour. *See also the Katadyn Survivor 06 Desalinator. The 06 desalinator costs less than the 35 and is only 2.5 lbs. But it also has just one forth the output of the 35 (2 hours per person per day just pumping water).