So, both surface and groundwater sources of water are important. Let us look at some basic difference between the two sources of water.

In many cases the ground water is preferable while some other times surface water is better. Ground water from a deep source is too saline to drink. On the other hand surface water with high turbidity is non-potable. Surface water also carries more water borne disease than the groundwater including the “river blindness disease”.

a] Some reasons why ground water is often more desirable than surface water:

1. Avaibility: Ground water storage is often orders of magnitude greater than the surface water. This is particularly true for alluvial aquifers (shallow aquifers comprised of unconsolidated sediments) and sedimentary basins. In some arid locations, streams are ephemeral (do not flow all year) making ground water source more important for water use.
2. Uniform chemical composition: The chemical composition of ground water is often less variable than the surface water.
3. Temperature: The temperature of ground water is nearly constant making it desirable for certain industrial applications – notably cooling methods.
4. Turbidity: Ground water is typically less turbid than the surface water.
5. Diseases: Ground water is often more free of water borne pathogenic organisms (malaria, salmonella, “river-blindness disease”, etc) and hence needs less water purification than surface water. These water borne deceases are by no means “in-control” and still represent a huge threat to large populations throughout the world.

b] Some reasons why Surface water is often more desirable thanGround water:

1. Cost: This is the most important factor. Surface water typically costs much less per gallon to use than ground water as expensive drilling is not required for surface water.
2. Availability: Some regions underlain by impermeable rocks will not yield significant volume of ground water. Example: unfractured basalt, granite and some metamorphic rocks.
3. Quality: Ground water typically has more salts than surface water and in some regions the salinity of ground water makes the water non potable. The salinity of ground water increases with depth due to increased solubility of most minerals at higher temperature.
4. Visibility: Surface water is visible while ground water is not.

1. Ground water: usually water associated with the saturated zone. A very common term for hydrogeologits or geohydrologists.
2. Surface water: water from streams, rivers, lakes etc, also studied by hydrogeologits and geomorphologists.
3. Soil water: usually refer to water associated with the “vadose zone”. A very common term for soil scientists and hydrogeologists.
4. Waste water: Typically sewage effluent and treated effluent. A very common term used by sanitary or environmental scientists.

B. Classification of water by Origin ( reference Donald White, 1960)

1. Juvenile water: Any water that is new to the hydrogeologic cycle, for example, emanating from magmatism, volcanism and metemorphism.
2. Metamorphic water: water produced deep within the crust (Juvenile water) resulting from degassing and hydration of minerals as they are metamorphically converted to more stable forms. for example Tremonite + calcite +quartx –> diopside + CO2 + water (not balanced); this water exist conceptually and may be volumetrically significant but it is not obtainable.
3. Meteoric water: water that has recently been associated with the hydrologic cycle and can return to the hydrologic cycle. This is water that recharges aquifers by precipitation. This is obviously the most common origin of all groundwater and extremely significant.
4. Magmatic water: water deriving from magmatism or melting of rocks (juvenile water). Note: All magmatic water is juvenile water. The standard of origin of oceans of from some magmatic source.
5. Phreatic Explotion water: This is geyser type of water emerging from below a volcano, incipent volcanic eruption, or some other hydrothermaly active sites. Most of this water is in fact metamorphically derived water.
6. Cometary water: there has been a controversy ranging since the 1980′s in the field of astronomy focussed upon the existence of microcomets that constantly bombard the earth. These comets have been :imaged” by modern spectroscopic satellite methods; however, astronomers are not always convinced of their reality. These collisions are so numerous that the microcomets (comets are mostly water and organic debris) can account for all the water in oceans. This is controvertial and one has to ask why Mars and the Moon are not covered with such oceans as those comets must have had strike their surfaces too.
7. Hydrothermal Water: This refers to hot and deep ground water. Due to high lithostatic pressure, water can stay within the liquid phase to amazingly high temperature (>600 oC). Most hydrothermal water has been shown to be meteoric in origin.
8. Fossil or Connate water: This was formerly referred to as “formational water” in petroleum field. They are water from great depths, usually as the result of petroleum extraction, and are usually brine in nature. Connate water was originally thought to represent ocean water buried with the rock. However, this now known not to be the case. These water do not isotopically or chemically match the sea water of any supposed geologic period and have been diagenetically altered. Their evolution is more important than their origin. Without human intervention (i.e. pumping) these fluids are typically isolated from the hydrologic cycle for very long time ( may have been for hundreds of millions of years)

C. Classification of water by Salinity:

The unit od measure is TDS = Total Dissolved Solids in milligrams per liter (mg/l) or parts per million (ppm)
Note: This is a loose definition and other sources may vary in range.

1. Fresh water: 0-1000 mg/l  TDS
2. Drinking water: 0-500 mg/l  TDS
3. Brakish water: 2000 – 20,000 mg/l  TDS
4. Normal marine water: 35,000 mg/l  TDS
5. Brine: 100,000 – 300,000 mg/l  TDS or 10-30% salt by weight.

If you are aware of any other classification scheme of water, please reply to the post. I will try to add them ASAP.