Water

Water is the source of life. Needless to mention the human body needs exactly 2.5L of water every day; even more if you are sweating. So the first thing to do before looking for food is of course finding water. An average human can live without water for about 3 days...
Make sure that you build your shelter next to a source of RUNNING water, or a big lake. Never camp next to a pond. You will get eaten alive by mosquitoes!

The images below show the WORST places to build a shelter. Stay away from theses places.

When you are looking for water, look for rivers and big lakes. Make sure the water is clear and there is no blue algae growing on the shores (That algae is toxic and sometimes deadly!) These are good examples of potentially safe water sources.

Here is a picture of the deadly blue algae:

These pictures were taken near Black Lake, Quebec.

 Don't forget to boil the water before drinking it. If you can't boil it, drink water only from rivers.