Natural water sources are a great way to supplement your fresh water supply. You can collect rainwater, water from rivers and streams, or even ponds or puddles. However, note that collected water should be presumed non-potable (non-drinkable); it often needs to be filtered for any use, and must be purified before drinking or otherwise consuming.
If you have other options for sourcing water, you'll generally want to use those first, as it's less work and the water quality is usually higher. However, local naturally-sourced water is more convenient if you are boondocking or otherwise far from civilization. In very limited locations, the water can be naturally very pure, but just looking at water isn't enough to guarantee that it's drinkable.
Rainwater
Rainwater can be collected in clean containers unless near pollutants of some kind. Wind-driven debris is common in receptacles. Indirect rainwater (suitable for non-potable uses) can be collected in large quantities off awnings and similar structures. Watch your vehicle during rain to see where the water collects.
Surface water
Water collected from open running sources, like rivers and creeks, should be assumed to be biologically suspect; it must be purified or used for non-potable uses.
Since water seeks lowest spots you might be able to see a source but not access it directly. A small cup or other receptacle can be strapped to a walking stick, bucket lowered on a rope, etc. Small transfer pumps can help collect water from shallow sources.
Water collected in puddles or ponds is the most likely to be contaminated with pathogens or to have concentrated pollutants. Use as a last resort and combine filtration and purification techniques.
