Possibly the most important thing you will need in a survival situation is water. There are things you can ensure without access to for a period of time, but water is not one of them. It is widely reported that three days is the maximum we can survive without consuming water, and that is likely a best case scenario. If you are sweating profusely, three days could very well be wishful thinking. Alternatively, there has been the occasional situation where people have managed to live longer than three days, but conservative estimates are best and pushing your luck when it comes to water is not recommended.
Unfortunately water is something that is at times taken for granted. It is so easily accessible in our current lives that it can be easy to forget that it someday might not be there. Ideally you will have purchased a supply of water to get you through, or at a minimum will have a portable filter or purification tablets. Even if you do have a healthy stash of bottled water, it is not the most easiest item to tote with you. Water is heavy and it is not realistic to expect to carry a lot. Because of this, you might need to look for water, and the first step in looking for it is knowing where to find it.
At is stands here and now, most of us rely on a municipality for water. This entails having safe, clean water piped into our homes that comes out of the faucet at the turn of a handle. While this is convenient, there are things to remember about municipalities. For example, they require large pumps to operate, pumps that are powered by electricity. They also require maintenance by trained personnel. Let's not forget the supplies necessary to treat water and make it safe for drinking. If the power goes out, hopefully a generator will be in place to get us by temporarily. Hopefully the supplies on hand will last. Hopefully the personnel required to run treatment facilities will not be headed out of dodge. Hopefully there will be no contamination issues. The key word here: hopefully.
If you are fortunate enough to have a well as a water source, you are still not out of the woods. Wells also require electricity to operate the pump, but this is something you can work to improve. Rather than depending on traditional electricity, you can add solar or manual implements to your well to allow for pumping when the power goes down. If you do not have a well, however, getting one can be quite costly. There are many other factors to consider, which will vary based on where you live. For example, the deeper the well must be, the more money it will cost to dig it. In some areas, old wells that have been out of use will have to be recertified before you can get electricity to them, which you may need temporarily until you are able to install a solar or manual option.
When municipalities fail and well water is not available, think about places in your home where water is present. One such example is the toilet tank reservoir. Provided you do not use bluing chemicals to give the water in the bowl a pretty hue, water from the reservoir can be removing and purified/filtered for drinking. Another possibility is your hot water heater, which holds a significant amount of water. Hot water heaters have a tap at or near the base for emptying, so you can drain water from there by using a bucket or hose. Over time, sediment collects in hot water heaters, so filtration will be necessary before you drink this water.
There may, and probably will, come a time when you will be forced to find and gather your own water. This can be done at locations such as ponds, lakes, creeks, rivers, rock quarries, and other such bodies of water. The problem with these is that bacteria may exist in the water, so filtering or purifying will be necessary. You will also have to consider the matter of transport we mentioned earlier; water is heavy and it splashes, so you really need some sort of easily portable enclosed container to move it about fruitfully and to keep it from evaporating.
Another option for water retention is collecting rainwater. Whether you have a cistern or a bucket, anything you are able to collect is better than nothing at all. You can create a water storage system ahead of time to collect and store falling rainwater or improvise one as needed by using items such as tarps to trap and direct rainwater into storage containers. The best containers for holding collected rainwater are 55 gallon drums that are food grade; do not store water in drums that once held chemicals. Rainwater will also need to be filtered due to the surfaces it has come into contact with during runoff.
Only in a dire emergency should you contemplate drinking water from a swimming pool. Due to the plethora of chemicals used to treat pool water, it is widely reported as unsafe for consumption. We've all swallowed a mouthful of pool water here and there and lived to tell the tale, but consuming copious quantities of pool water is likely a different story. As time passes, the effect of chlorine on pool water will diminish and growth of algae will occur. If you do attempt to drink pool water, be sure to do so at your own risk and only after purifying and filtering it. Also unsafe is saltwater. Drinking saltwater leads to further dehydration due to the salinity of it, which is higher than what the human body can pass through the kidneys. If you drink saltwater, you will have to urinate far more than normal more to pass it, actually becoming more dehydrated in the process. In small doses, salt is necessary, but large doses can be fatal.
When you start thinking about your survival needs, think about water. Make plans to acquire, store, and transport it as well as for purifying and filtering it. Dehydration is a real concern and once you become dehydrated, your ability to think clearly can become compromised, leading your search for acceptable water to possibly derail. Take initiative to plan for your water needs now, before it is too late and you find yourself up a (dried up) creek (bed).