What does "approximately" mean in the passage?

Directions: Read the passage carefully and answer the question that follows.

Water covers three-fourth of the surface of the earth, approximately. Over 97 per cent of the total water supply is contained in the oceans and other saline bodies of water and is not readily usable for most purposes. Of the remaining 3%, a little over 2% is tied up in ice caps and glaciers. Thus, for their general livelihood and the support of their varied technical and agricultural activities, humans depend upon the remaining less than 1% of water found in freshwater lakes, rivers and groundwater supplies. Water is mostly used for industrial and municipal purposes. In order to ensure the quality, it is important to monitor the water supply throughout all of its aspects. Rain water is the purest form of naturally occurring water. However, water is distributed in the nature in different forms such as river water, spring water, rainwater and mineral water.