A good way to indicate a water source is to get on an elevated surface and and look for indentions in the earth or trees. The indention shows that there is a low area or gap from surface to surface which, in turn, shows path of a water-way or past water-way.
However, be careful this could only show a ditch that only drains water when it rains.
One method of collecting water is to dig for water. Look for dry creek beds, sandy bottom lands or ravines. They may have water below the surface. Simply dig a hole until water begins to seep into it. Gather your liquid with a container or a piece of cloth.
The water is usually pure but filter and purify it.
To make a simple water filter you can take three sticks. Tie them in tee-pee formation and tie three pieces of cloth one above the other. Put a container to catch the water at the bottom. Pour the water through and it will help filter out sediment.