Category Archives: SERE

Insect Indicators of Water

Photo by Ralph Haering

Photo by Ralph Haering

To Do Today:

Insect Indicators of Water

In general, more life means water and insect numbers can be closely related to water and food sources. In many arid areas, you can tell how close you are to a water source by the number of flies present. Dragonflies, bees, and mosquitoes are also water-loving species that can signal the source is near.

  • Flies. Dense clouds of flies swarming in a generally focused area, particularly in the desert, may indicate damp soil or soil where standing water was present only a short time previously. It is almost always worth digging a shallow hole in a low spot near the flies to investigate the possibility of a water source.
  • Bees. Bees presence may be a sign of water. Rarely will a hive of wild bees be more than 3 or 4 miles from fresh surface water. A bee can generally fly 1 mile in 12 minutes. The water source may be small, hidden, or difficult to reach. Use other indications to confirm and locate the water source.
  • Ants. Most ants need water, so if you see a steady column of small black ants climbing a tree trunk and disappearing into a hole, it is highly probable that you fill find a hidden reservoir of drinkable water. This can be proved by dipping a long straw or thin stick down the hole into which the ants are going. If wet, then water is there. To get the water, do not chop into the tree. If the hole is very small enlarge it with your knife-point at the top. Make a mop by tying grass or a rag to a stick. Dip the mop into the water and squeeze into a container. Another method is to take a long hollow straw and suck the water you need from the reservoir. These natural tree reservoirs are very common in dry areas, and are often kept full by the dew which condensing on the upper branches of the tree, trickles down into the reservoir inside the tree. Water reservoirs are very common in the She-Oaks (casuarinas) and many species of Wattle.
  • Mason Flies. These large, hornet-like creatures are a certain indicator of water. If you see a mason fly’s building in an area you can be sure that you are within a few hundred yards of a soak of wet earth. Search around carefully and you will see the mason fly hover and then suddenly drop to the ground. If you examine the place where it landed, you will find the soil is moist and that she is busy rolling a pellet of mud for building. By digging in this area, a few inches or at most a couple of feet, you may find drinkable water.

Information contained on this website is for general information and educational purposes only. Please refer to our Disclaimer and Terms and Conditions before attempting any technique described herein.

Water Procurement

Photo by Frank Michaux

To Do Today:

  • PT – Cross train: Bike/Row/Swim for 60-90 min at low
    to moderate intensity.

Water Intake

Thirst is not a strong enough sensation to determine how much water you need. The best plan is to drink water utilizing the OVER DRINK method. Drink plenty of water anytime it is available and particularly when eating.

Dehydration is a major threat. A loss of only 5 % of your body fluids causes thirst, irritability, nausea, and weakness; a 10% loss causes dizziness, headache, inability to walk, and a tingling sensation in limbs; a 15% loss causes dim vision, painful urination, swollen tongue, deafness, and a feeling of numbness in the skin; also a loss of more than 15% body fluids could result in death.

Your water requirements will be increased if:

  • You have a fever.
  • You are experiencing fear or anxiety.
  • You evaporate more body fluid than necessary (i.e., not using the proper shelter to your advantage),
  • You have improper clothing.
  • You ration water.
  • You overwork.

Collecting Incidental Water

During movement, you may have to ration water until you reach a reliable water source. Incidental water may sometimes provide opportunities to acquire water. Although not a reliable or replenished source, it may serve to stretch your water supply or keep you going in an emergency. The following are sources for incidental water:

  • Dew. In areas with moderate to heavy dew, dew can be collected by tying rags or tuffs of fine grass around your ankles. While walking through dewy grass before sunrise, the rags or grass will saturate and can be rung out into a container. The rags or grass can be replaced and the process is repeated.
  • Rainfall. Rainwater collected directly in clean container or in plants that contain no harmful toxins is generally safe to drink without disinfecting. The survivor should always be prepared to collect rainfall at a moments notice. An inverted poncho or tarp works well to collect rainfall.

Water Quality

The first choice for water should obviously be potable water from treated sources such as municipal water systems, proven well-water, etc. Potable only indicates that a water source, on average over a period of time, contains a minimal microbial hazard and likelihood of illness is acceptable. Tap water is not guaranteed to be safe in the event of a large scale emergency and should be disinfected or filtered as described below. If visible taps are dry, attempt to locate lower taps in depressed geography (i.e., homes/taps in lower locations) as water in pipes will naturally flow to lower places in the distribution system.

Almost all water without treatment, contains minerals, toxins, and pathogens. Some of these, consumed in large enough quantities may be harmful to human health. Pathogens are the primary concern. Pathogens are divided into Virus, Cysts, Bacteria, and Parasites. Certain pathogens are more resistant to chemicals and small enough to move through microscopic holes in equipment (i.e., T-shirt, parachute). Certain pathogens also have the ability to survive in extremely cold water temperatures. Pathogens generally do not live in snow and ice. The following methods can be used to improve water quality in a survival/SERE situation:


Water disinfection removes or destroys harmful microorganisms. Giardia cysts are an ever-present danger in even pristine surface water throughout the world. By drinking non-potable water you may contract diseases or swallow organisms that could harm you. Examples of such diseases or organisms are: Dysentery, Cholera, Typhoid, Flukes, and Leeches. Impure water, no matter how overpowering the thirst, is one of the worst hazards in a survival situation.

The first step in disinfecting is to select a treatment method. Two methods are as follows:

  • Heat. You must bring the water to a rolling boil before it is considered safe for human consumption and is the most preferred method. Bringing water to the boiling point will kill 99.9% of all Giardia cysts. The Giardia cyst dies at 140F/60C and Cryptosporidium dies at 150F/65C.
  • Chemicals. There are numerous types of chemicals that can disinfect water but some chemicals may not destroy Cryptosporidium. The most common are iodine tablets, chlorine bleach, iodine solution, and betadine solution. In a survival situation, you will use whatever you have available.


Water purification is the removal of organic and inorganic chemicals and particulate matter, including radioactive particles. While purification can eliminate offensive color, taste, and odor, it may not remove or kill microorganisms.

  • Expedient Filtration. Filtration purifying is a process by which commercial manufacturers build water filters. The water filter is a three tier system. The first layer, or grass layer, removes the larger impurities. The second layer, or sand layer, removes the smaller impurities. The final layer, or charcoal layer (not the ash but charcoal from a fire), bonds and holds the toxins. All layers are placed on some type of straining device and the charcoal layer should be at least 5-6 inches thick. Layers should be changed frequently and straining material should be boiled. Remember, this is not a disinfecting method, cysts can possibly move through this system.

water filter

  • Commercial Water Filtration. Understanding what a filter can do is the first step in safeguarding against illnesses so be sure to investigate the type and appropriate uses of your filter. A filter that has a .3 micron opening or larger will not stop Cryptosporidium. A filter system that does not release a chemical (i.e., iodine) may not kill all pathogens. A filter that has been overused may be clogged and usage may result in excessive pumping pressure that can move harmful pathogens through the opening.


Distillation of drinkable water using the solar still method can be used to reduce and eliminate toxins and harmful organisms. Solar stills are designed to supplement water reserves and contrary to belief, one solar still will most likely not provide enough fluid to meet the daily requirement for water. Build multiple units if possible.

Above-Ground Solar Still. This device allows the survivor to make water from vegetation.

above grade solar stillTo make the above-ground solar still, locate a sunny slope on which to place the still, a clear plastic bag, green leafy vegetation, and a small rock. Construction:

  • Fill the bag with air by turning the opening into the breeze or by “scooping” air into the bag.
  • Fill the bag half to three-quarters full of green leafy vegetation. Be sure to remove all hard sticks or sharp spines that might puncture the bag.
  • Do not use poisonous vegetation. It will provide poisonous liquid.
  • Place a small rock or similar item in the bag.
  • Close the bag and tie the mouth securely as close to the end of the bag as possible to keep the maximum amount of air space. If you have a small piece of tubing, small straw, or hollow reed, insert one end in the mouth of the bag before tying it securely. Tie off or plug the tubing so that air will not escape. This tubing will allow you to drain out condensed water without untying the bag.
  • Place the bag, mouth downhill, on a slope in full sunlight. Position the mouth of the bag slightly higher than the low point in the bag.
  • Settle the bag in place so that the rock works itself into the low point in the bag.
  • To get the condensed water from the still, loosen the tie and tip the bag so that the collected water will drain out. Retie the mouth and reposition the still to allow further condensation.

An above ground solar still.

  • Change vegetation in the bag after extracting most of the water from it.
  • Using several gallon ziploc bag instead of trash bags is a more efficient means of construction.

Below-Ground Solar Still. Materials consist of a digging stick, clear plastic sheet, container, rock, and a drinking tube.

solar stillTo Construct:

  • Select a site where you believe the soil will contain moisture (such as a dry stream bed or a low spot where rainwater has collected). The soil should be easy to dig, and will be exposed to sunlight.
  • Dig a bowl-shaped hole about 1 meter across and 24 inches deep.
  • Dig a sump in the center of the hole. The sump depth and perimeter will depend on the size of the container you have to place in it. The bottom of the sump should allow the container to stand upright.
  • Anchor the tubing to the container’s bottom by forming a loose overhand knot in the tubing. Extend the unanchored end of the tubing up, over, and beyond the lip of the hole.
  • Place the plastic sheet over the hole, covering its edges with soil to hold in place. Place a rock in the center of the plastic sheet.
  • Lower the plastic sheet into the hole until it is about 18 inches below ground level. Make sure the cone’s apex is directly over the container. Ensure the plastic does not touch the sides of the hole because the earth will absorb the moisture.
  • Put more soil on the edges of the plastic to hold it securely and prevent the loss of moisture.
  • Plug the tube when not in use so that moisture will not evaporate.
  • Plants can be placed in the hole as a moisture source. If so, dig out additional soil from the sides.
  • If polluted water is the only moisture source, dig a small trough outside the hole about 10 inches from the still’s lip. Dig the trough about 10 inches deep and 3 inches wide. Pour the polluted water in the trough. Ensure you do not spill any polluted water around the rim of the hole where the plastic touches the soil. The trough holds the polluted water and the soil filters it as the still draws it. This process works well when the only water source is salt water.
  • Three stills will be needed to meet the individual daily water intake needs.

Preparing a below ground solar still


Sedimentation is the separation of suspended particles large enough to settle rapidly by gravity. The time required depends on the size of the particle. Generally, 1 hour is adequate if the water is allowed to sit without agitation. After sediment has formed on the bottom of the container, the clear water is decanted or filtered from the top. Microorganisms, especially cysts, eventually settle, but this takes longer and the organisms are easily disturbed during pouring or filtering. Sedimentation should not be considered a means of disinfection and should be used only as a last resort or in an extreme tactical situation.

Hazardous Fluids

Survivors have occasionally attempted to augment their water supply with other fluids, such as alcoholic beverages, urine, blood, or seawater. While it is true that each of these fluids has a high water content, the impurities they contain may require the body to expend more fluid to purify them. Some hazardous fluids are:

  • Sea water. Sea water in more than minimal quantities is actually toxic. The concentration of sodium and magnesium salts is so high that fluid must be drawn from the body to eliminate the salts and eventually the kidneys cease to function.
  • Alcohol. Alcohol dehydrates the body and clouds judgment. Super-cooled liquid, if ingested, can cause immediate frostbite of the throat, and potential death.
  • Blood. Blood, besides being salty, is a food. Drinking it will require the body to expend additional fluid to digest it.
  • Urine. Drinking urine is not only foolish, but also dangerous. Urine is nothing more than the body’s waste. Drinking it only places this waste back into the body, which requires more fluid to process it again.

Information contained on this website is for general information and educational purposes only. Please refer to our Disclaimer and Terms and Conditions before attempting any technique described herein.

Rafts and Rope Crossing


Photo by John Helms

To Do Today:

  • PT – Cardio/Strength – 4 sets of: 400m run/10 dips/400m run/50 situps/400m run/10 pullups/400m run/50 pushups. Warm up and cool down distance at discretion.
  • Practice the floatation methods described below in a pool or open water until mastered.
  • Review rope care in the General Rescue Manual 2006 Sec-5-8.
  • Review climbing knots Here.

Closed Cell Sleeping Pad Raft

Construction of a closed cell sleeping pad raft is time-consuming. This type of raft should not be employed tactically (i.e., an attack) but used for logistical purposes (i.e., evacuating stretcher cases, transporting supplies). Use the following steps to build the raft:

  • Wrap closed cell sleeping pads around sturdy sticks.
  • Use parachute cord and square knots to tie the pads securely in place and to lash stick ends together in a rectangle.

isomatraftThe sleeping pad raft pictured can support several hundred pounds. However, the cargo will get wet if not properly waterproofed.

Poncho/Tarp Raft

A poncho or tarp raft can support two swimmers and their equipment and is well suited for long crossings. Use the following steps to build a poncho raft:

  • Inspect two ponchos/tarps and ensure they are serviceable.
  • Lay one poncho or tarp flat on the ground, with the hood-side up (if a hood is present).
  • Cinch the hood tightly to form a gooseneck or tie in a knot.


  • Pad sharp edges of equipment and place the equipment in the center of the poncho.


  • Place the second poncho over the equipment, rubber side up, and hood facing down.
  • Snap the edges of the two ponchos together.


  • Roll the edges toward the equipment.
  • Roll the edges into pigtails and tie them off.

poncho roll

  • Pull the pigtails together over the top and lash them securely.


  • Protect the raft from brush punctures while placing it in the water. Swim across the water obstacle while security elements are covering the far shore.


Pack Raft

You will need two waterproofed packs and two rifles/rigid poles. The following steps are guidelines to construct a pack raft:

  • Place two packs side-by-side with the pack frames on the deck. The tops of the packs are opposite of each other.
  • Loosen the main compartment straps on both packs.
  • Insert one rifle on each end between the straps and the packs.
  • The muzzles are opposite of each other. The rifles serve as one means to secure the packs together. Place the front sight post under the top flap.
  • Tighten the straps so that the rifles and packs are secure.
  • Take the excess strap on the inner side of each pack and secure it to the opposite pack to better secure the two packs together.
  • Take the excess straps on the outer sides of the packs and use those straps as safety lashing for the rifles.
  • Tuck the excess straps and check to make sure the rifles and packs are secure.


Single-Rope Bridge

A single-rope bridge offers a temporary and quick way to cross small rivers. It also provides extra security while crossing swift waters. At night, it prevents straggling, and guides larger units precisely from one side of the river to the other side. If crossing a river at night, plan for at least one single-rope bridge. If you are crossing a river with swift currents or water depths above 4 feet, the unit is carrying sufficient rope to span the crossing site, and the tactical situation permits, secure the rope on near and far banks to provide a hand-hold for crossing swimmers. This reduces the time required for the entire unit to cross and provides a degree of comfort/confidence for poor swimmers. Use a squad-sized bridge team to construct a single-rope bridge. Station several strong swimmers at the water’s edge to help anyone who has trouble crossing.

Nylon rope is normally coiled in 120 foot lengths. It is 0.6 inches in diameter and has a breaking strength of about 3,840 pounds. Over time, a nylon rope can stretch to as much as one-third more than its original length and stretching weakens the rope. If the rope is stretched, discard the rope or use it for light tasks. To prolong the life of a nylon rope, do not step on it or drag it on the ground. Pad the rope in places where it contacts rocks or sharp corners. Do not leave the rope knotted or stretched longer than necessary. Dry rope as soon as possible. Single-rope bridge construction is as follows:

  • Tie a sling rope around your waist using a square knot and two, separate half hitches. See the link above for detailed information on knots.


  • Attach a locking steel carabiner to the sling rope.
  • Tie a bowline knot in the running end of the bridge rope and attach it to the carabiner.
  • Temporarily secure the other end of the rope to a tree on the near shore.
  • Enter and cross the water. Carry only your weapon and ammunition.
  • Exit the water on the opposite shore.


  • Prepare your weapon for use. Unhook the bridge rope from the carabiner at your waist, and tie the bridge rope to a sturdy tree using a round turn and two half hitches.


  • Conduct a box reconnaissance of the opposite shore.
  • On the near shore, have another swimmer prepare to tighten the rope. That swimmer should place a transport tightening system in the bridge rope by tying a double butterfly knot and placing two carabiners on the butterfly knot.


  • The swimmer should pass the running end of the bridge rope around the downstream side of the near shore anchor point and through the two carabiners.
  • Pull the butterfly knot approximately one-third of the distance across the river.
  • Secure the bridge rope to an anchor point using a round turn and two half-hitches.
  • On the near shore, the person helping you should pull the slack out of the bridge rope until the butterfly knot is back on the near side. The bridge rope is then tied off against itself using two half hitches with a quick release in the last half hitch.

The single-rope bridge must be as tight as possible so it will not sag when used. If you lose your footing and fall into the water, swim with the current to the closest shore. Swimming against the current is dangerous and quickly causes fatigue.

High and Dry Crossings

If the single-rope bridge is high enough, suspend yourself below the single-rope bridge and above the water. Use the following steps to suspend yourself from a single-rope bridge and then pull yourself across the water:

  • Tie a sling rope around your waist using a bowline. Ensure that the knot is tight.


  • Attach a carabiner through the bowline’s loop. The carabiner’s gate faces up.
  • Secure your helmet, if any. Face the single-rope bridge with your left shoulder toward the far shore.
  • Grasp the bridge rope in both hands.
  • Swing your body beneath the single-rope bridge with your head toward the far shore. Cross your ankles above the bridge rope.
  • Arch back until the carabiner contacts the bridge rope. Connect the carabiner to the bridge rope. Allow the carabiner to bear your body’s weight.
  • Pull yourself across the single-rope bridge, hand over hand, to the far shore.

sling5Swift Current Crossings

A single-rope bridge prevents being knocked down and swept away by a swift current. Use the following steps to move through a swift current:

  • Tie one end of a sling rope around your waist using a bowline.
  • Tie the running end of the sling rope in another bowline, and attach a carabiner to the bowline’s loop.
  • Step up to the bridge. Face upstream.
  • Hook the carabiner to the single-rope bridge.
  • Walk sideways into the river while grasping the bridge rope in both hands.
  • Use the single-rope bridge for balance and remain standing, if possible.
  • Continue to move sideways through the river to the far shore.

Slow Current Crossings

If you face little or no current, it is not necessary to hook up to a bridge rope with a carabiner. Lie on your back in the water beneath the single-rope bridge. Support your body weight with your waterproofed pack. Use the bridge rope and pull yourself hand over hand across the river.

Removal of Rope Bridges

If you are the last person waiting to cross, pull on the standing end of the rope to release the knot, then tie the rope around your waist using a bowline. The others on the far shore will pull you through the water.

Information contained on this website is for general information and educational purposes only. Please refer to our Disclaimer and Terms and Conditions before attempting any technique described herein.