Don't worry. This entry won't be quite as long as my last few have been because I am talking about H2O. That's right: water.
Water is essential to human life. The body is 60% water, where the other 40% is comprised of intracellular fluid and extracellular fluid. To survive, you must continue to hydrate yourself with water. If you stop drinking water, you will begin to dehydrate. Dehydration is defined as an excessive loss of body fluid. Common forms of dehydration include the loss of electrolytes (sodium in particular), water, and a combination of both. I'm not going to spout off much scientific jargon because jargon isn't what will save your life. Water will save your life. Drink it!
Your body loses fluid through heat, cold, stress, defecation, and exertion. In nominal temperatures (68 degrees F), the body loses 2-3 quarts (liters) of water a day. Therefore, you need to replenish said amounts. You may lose more or less depending on various factors, such as temperature, humidity, physical exertion, or other factors such as diarrhea.
The result of dehydration, which is the inadequate resupply of water into your system, is shock. It also reduces your ability to do even the simplest of tasks, like tying a knot.
To prevent dehydration, you should take small sips of water regularly, even if you are not thirsty. Thirst does not indicate how much water you need. Moreover, thirst is a sign that you are already dehydrated.
Here is a simple body fluid loss percentage with the results. At 5% body fluid loss, you are thirsty, irritable, nauseated, and you may feel weak. At 10%, dizziness occurs, followed by a headache, inability to walk, and a tingling sensation in the limbs. At 15%, your vision suffers, it hurts to urinate, your tongue swells, deafness can occur, and you experience a numb feeling in your skin. If you lose more than 15% body fluid due to dehydration, YOU WILL DIE!
It's always been said to me that your urine should be clear, or close to it. However, if you can pee out 1 gallon a day, you are doing your part to stay hydrated. Obviously, in high heat, you should increase your water intake to 4-8 gallons daily, depending on how hot it is, exposure, and your level of activity. When I went to Boy Scout Camp in late July, 2009, it was 110 degrees (dropping only to 90 in the evening), and there was no wind. I must've filled my 1 quart nalgene bottle 30 times each day! Still, a lot of people suffered from heatstroke, which is the body's inability to cool itself off. Basically, it's like an overheating engine, which is BAD!
Now, I've been severely dehydrated before, so I know what it's like to experience it. It sucks! My judgment was impaired, I became clumsy, and couldn't see straight. My ability to navigate using my compass and map went straight down the toilet. Fortunately, my wife was there and was able to help me back to camp without me getting killed.
In your 72 hour kit, is important to carry 3 days worth of water, which amounts to about 3 gallons. These should be in sealed containers that you did not open (bottled water). The reason for that is algae growth. When the water is bottled at the factory, it is a sterile environment. Your kitchen, or your garden hose, is not. Using your own containers introduces all sorts of opportunities for little bacterial things to grow, and mold to occur. Mold and bacteria = very VERY bad. You may expect diarrhea if you drink contaminated water, at the least.
Should you find yourself in a situation where you've got a long way to go, and you have run out of water, then you have another option; purification or filtration. I recommend buying a water filter or purifier (whatever you decide is up to you - makes no difference to me). This will allow you to collect water from any source and use it. From mud puddles to rivers, to streams, to even used bath water, a filtering device will remove contaminants and make it safe to drink. I would avoid sewage or the water IN the toilet bowl. Water from a toilet tank is safe. To put one of these filtration devices to the test, a friend of mine and I pumped Mt Dew through a MSR water filter. Water came out. No hint that it was soda just seconds before.
You might also carry iodine tablets designed for water purification as an alternative to filters. Additionally, boiling water will also kill bacteria and make it safe to drink. Double your safety by first filtering and then boiling.
Remember that dehydration is your enemy and will render you nothing more than a boat anchor if you are trying to make it home safe. Stay hydrated. It is of the utmost of importance.