How can you boil large quantities of drinking water in an emergency without consuming gigantic amounts of fuel? The answer is to recycle the energy. A practical device for doing that is inexpensive and simple to build.

   Fig. 1 shows a counterflow heat exchanger, with a boiler on the right end, having inputs and outputs on the left. The heat exchanger consists of a 1 in. (2.5 cm) input pipe placed inside a 3 or 4 inch (7 - 10 cm) output pipe made of the same metal. For short-term use, aluminum, brass or non-galvanized steel works, but stainless steel is best for permanent installations.

   Place the small pipe inside the large one, leaving a 1 in. (2.5 cm) space between the end of the small pipe and the cap on the large one. The unit is sloped slightly toward the boiler. Input water should be cleaned first. This device is not a still. Therefore it will not separate sewage or chemical contaminants from the water. It is merely an efficient way to boil water.

How it works:

1. Water is input at pipe (a), and
2. Held in the water tank. Always keep water in this tank so the boiler doesn't run dry, which may damage the boiler.
3. A filter helps keep the boiler clean. In an emergency you can use bath towels or other clean cloth.
4. Water enters the heat exchanger at (b) and moves toward the boiler through inner pipe (d), where it boils, and then returns through outer pipe (e) to output valve and spigot (s)

1. As heated water exits through the outer pipe, input water in the inner pipe is heated to boiling. This lengthens the time that flowing water remains at high temperature.
2. A thermometer (t) is located about 10 feet (3 meters) from the boiler. This should remain at boiling temperature, 212º F. (100º C.)
3. To raise the temperature, slow down the water flow with valve (s), or add more heat at the boiler.
4. To lower the temperature, run the water faster, or turn down the heat.
5. The goal is to keep the flowing water at boiling temperature for one or two minutes. (Check with your local health authorities to see how long the water needs to be boiled.) Simply running water through the device will not guarantee that it is safe. The operator must maintain the heat input and water flow correctly so that the flowing water will remain at boiling temperature the required time.
6. Input pipe (c) should be about 3 ft. (1 m) long, providing continuous water pressure into the boiler. It purposely has no valves. Rather, the head of water provided by its height acts as a safety valve. Should the boiler overheat, steam will blow backwards up into the water tank.
7. If hot water comes out of Spigot (s) then the unit is too hot. The water should be slightly warm, because the unit is not 100% efficient.
8. The unit is made for continuous operation. So whenever it is started cold, put a cap full of bleach in the input water, and then run it until you cannot taste the bleach in the output.

   The heat exchanger should be a minimum of 40 ft. (12 m) long, but will work better if longer, above 100 ft. (30 m).

   To conserve heat, it is insulated (i). Conventional insulation can be used if it is kept dry. Better yet, Fig. 2 shows a cross section at the middle of the exchanger without insulation (f). It is covered with 3 ft (1 m) of dry dirt (m). Add a layer of plastic sheeting (p), overlapped like shingles to shed surface water. On top is a protective layer of dirt (k). This arrangement will protect the boiler, and trap heat near the exchanger to make it more efficient.

   Any heat source with appropriate fixtures needed to heat the boiler will work. Gas, oil, LP gas, even wood in an emergency. Solar can also be used by concentrating sunlight onto the boiler.

   If you have communications to people in disaster areas, direct them to this website.

   Now that's exciting, isn't it!