The notion about water resources has wide and narrow sense.
In the wide sense, this is all waters of hydrosphere that are included in the rivers, lakes, glaciers, seas and oceans and also in the underground horizons and atmosphere. It can be defined as a huge, inexhaustible and it is no wonder. Because the World Ocean occupies 361 million km2 (about 71% of all planet), and glaciers, lakes, reservoirs, marsh, rivers occupy 20 million km2 (15 %). As a result, hydrospheric total capacity is evaluated in 1390 million km2. You can easily calculate, that one inhabitant of the Earth has 210 million m2 of water. This quantity of water would be enough for the big city during one year! You can also consider the opportunities of the resources usage. 96,4% of water fall on the World ocean from the hydrosphere total capacity; glaciers and ground waters include much water (1,86%) from the land water. Their usage is possible but it is difficult.
That is why, when we say about water resources in the narrow sense, wemean an available fresh water, whichcompound only 2,5 % of the hydrosphere total capacity.