1. We usually find water in lakes, rivers, seas and oceans. Water can also be ice (snow), steam and just water.
2. Potable (drinking) water is fresh water, water without salt. Water is seas and oceans, for instance, is not potable, because it contains salt.
3. No doubt, it is. Water is definitely becoming scarcer in certain places. Due to climate change some reservoirs are drying up. Besides, uses of water include a lot of activities, for example agricultural, industrial, household, recreational and environmental, that's why we are running out of water in some places. Pollution is also an important problem for water as natural resource.
4. Water-poor countries use importation of goods as the primary method of importing water.
5. Changing composition of natural water resources is a global problem nowadays. Harmful waste from factories poisons water and makes it unsuitable for drinking and dangerous for all living organisms. For a long time people didn't care about the environment, that's why foreign molecules wedged into the composition of natural water resources.