Potable water (or "drinking water") is a subset of fresh water. It is clean and safe enough for human consumption. Municipal water supplies and water kiosks generally fall into this category, and commercially bottled water will always fall into this category.
Non-potable water is water that is not (or not known) to be safe for human consumption. Water from natural sources (rivers, streams, etc.), or other water that is not known to be potable, must be filtered and purified prior to use for human consumption.