Fresh water is vital to the lives of many plants and animals, including humans. Most of this water is made available to land-based life by precipitation in the forms of rain and snow.
On land, water will either:
1. Remain frozen as in the ice sheets of the poles and in mountain glaciers.
2. Form surface water in lakes, rivers and reservoirs
3. Seep into the ground to form an aquifers in permeable rock or materials such as gravel or sand.
Both surface water and underground water accounts for less than three-quarters of a percent al the water on earth, but are the made sources of drinking water. The choice of which source to use comes down to availability and/or personal taste.
The source of rivers and streams may be a mountain spring, a lake or melting ice and snow. As the river flows it will pick up additional water from run-offs and aquifers, growing in size until it reaches a large body of water such as the sea. Fast-flowing water near the source of a river will be full of oxygen and contain very few impurities, but as it flows it will accumulate sediment and other deposits, possibly through industrial contamination. Most of the tap water available in the developed world is sourced from running water, but requires treatment before becoming drinkable.
Both well water and spring water will be sourced from aquifers. A spring is formed when the aquifer meets a non-permeable rock and the water is forced out, or where ground depressions are below the water table. Because aquifer water has seeped through the ground, it is naturally filtered but picks up soluble minerals on the way. The spring water that is sold will often be described as mineral water, with the minerals it contained depending on the location of the source. Such water is usually not treated with chemicals before being consumed, and many consumers will report that spring water tastes best.
Well water is obtained by sinking holes into the ground to reach the water table. It initially has the same properties as spring water, but because it is not flowing it is more prone to contamination and drinkers should take care to protect their source.
In the developed world we are lucky to be able to chose between these sources of water, but hygiene standards are such that either spring or tap water is safe to drink - it all comes down to a matter of taste.