You may be thirsty, but that stream or pool of water on your camp site is probably not safe to drink. Not at least until you have made some preparations. It is always best to assume the worst when it comes to drinking water out in the field, you have no knowledge of who may have used the site before you, this includes animals as well as other people.
Standing water such as pools and small lakes can be particularly risky as there is a danger of stagnant water or water that has had contaminants leech into the water from the ground around it. If you are using an established camp site and those before you have been digging latrines in the area such water could provide a severe health risk.
Assumption that the water is safe to drink may ruin your camping trip with stomach upsets or worse. It is far better to be a little patient and either boil any available water or to use a water purification device. Even free flowing water, from a stream or river may appear to be safe, but again, far better to be cautious, after all, there could be an animal carcass lying in the water further upstream.
There are some sources of water that can be considered safe to drink and they are either rain water that you catch yourself, or fast running stream water as long as you are above creature level. The last is particularly true if you are camping in areas where sheep or deer are prevalent.
If you are not taking sufficient drinking water with you on your camping trip then you should make sure you pack some water purification tablets or a water filter capable of filtering water to drinking quality standards. Or of course fire making facilities and something to boil your water in. If you are backpacking it is likely you will have a small stove with you and this will be suitable for water boiling.
It is important that water you are purifying by boiling really does boil. Do not be tempted to just heat the water as this could make things worse for you. Make sure the water is bubbling away and plenty of steam is rising from it’s surface. Also allow to boil for a couple of minutes after boiling point is reached.
you should also take with you sufficent containers to hold your drinking water once it has been purified or boiled and such containers should have tightly sealing caps or lids so that the water remains safe until you drink it. If you are in a large group, make sure that someone is put in charge of all drinking water so that no cross contamination takes place and that non purified water does not get mixed in with the purified.
Make sure the stay you have in your camp site is an enjoyable one and do not rush to drink that tasty looking water until it has been made safe for consumption.