We can conclude from the writer's statement that ……………

Providing water for man and his industry grows daily more difficult. Almost always the demand is for fresh water, but the proportion of the Earth's water in rivers and streams is extremely small. If the Antarctic ice cap were to melt, it would feed all the rivers for 800 years. Although several schemes have been suggested for utilizing this source, none have so far been practical. Far more promising is the tapping of the large supply of underground water or the desalination of sea water. Yet, whichever means is used, managing our supply of water is a technical challenge of huge and urgent importance.