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Surface water is naturally replenished by precipitation and naturally lost through discharge to evaporation and sub-surface seepage into the ground. Although there are other sources of groundwater, such as connate water and magmatic water, precipitation is the major one and groundwater originated in this way is called meteoric water.
Classification of surface water quality 
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The field of hydrometry classifies surface water quality into five categories:
- Class 1 is extra-clean fresh surface water resource used for conservation, not necessarily required to pass through a water treatment process, and requiring only an ordinary process for pathogenic destruction and ecosystem conservation where basic organisms can breed naturally.
- Class 2 is very clean fresh surface water resource used for consumption, which requires an ordinary water treatment process before use, for aquatic organism of conservation, fisheries, and recreation.
- Class 3 is medium-clean fresh surface water resource used for consumption, which requires passing through an ordinary treatment process before use for agriculture.
- Class 4 is fairly clean fresh surface water resource used for consumption, but requires a special water treatment process before use for industry.
- Class 5 is the source which is not classified in class 1-4 and used only for navigation.
Definition: Surface water is taken from the lakes, rivers, waterfalls and sea. It plays the largest role of shaping the geography of land.
Conjunctive use of ground and surface water 
Surface and ground water are two separate entities, so they must be regarded as such. However, there is an ever-increasing need for management of the two as they are part of an interrelated system that is paramount when the demand for water exceeds the available supply (Fetter 464). Depletion of surface and ground water sources for public consumption (including industrial, commercial, and residential) is caused by over-pumping. Aquifers near river systems that are over-pumped have been known to deplete surface water sources as well. Research supporting this has been found in numerous water budgets for a multitude of cities.
Response times for an aquifer are long (Young & Bredehoeft 1972). However, a total ban on ground water usage during water recessions would allow surface water to better retain levels required for sustainable aquatic life. By reducing ground water pumping, the surface water supplies will be able to maintain their levels, as they recharge from direct precipitation, runoff, etc.
See also 
- Optimum water content for tillage
- Environmental Persistent Pharmaceutical Pollutant EPPP
- Applied Hydrogeology, Fourth Edition by C.W. Fetter.
- R.A. Young and J.D. Bredehoeft Digital simulation for solving management problems with conjunctive groundwater and surface water systems from Water Resources Research 8:533-56
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