Assessments of water resources and their management

1. What are the resources of water available?

About 97% of the water on the Earth is salt water and only 3% is fresh water; slightly over 2/3 of this is frozen in glaciers and polar ice caps. The remaining unfrozen freshwater is found mainly as groundwater, with only a small fraction present above ground or in the air. The only natural input to any surface water system is precipitation within its watershed, the total quantity of water in that system at any given time is also dependent on many other factors.

Storage capacity include lakes, wetlands and artificial revservoirs, the permeability of the soil beneath these storage bodies, the runoff characteristics of the land in the watershed, the timing of the precipitation and local evaporation rates. All of these factors also affect the proportions of water loss. Water reclamation or wastewater reuse is the process of co-use instead of single use of freshwater supplies which can be a water-saving measure. When used, water is eventually discharged back into natural water sources, it can still have benefits to ecosystems, improving streamflow, nourishing plant life and recharging aquifers, as part of the natural water cycle converting wastewater into water that can be reused for other purposes⁴.

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