Sentence:  The best chance , of course , is offered by gently sloping terrain where the <WSD>water</WSD> remains close to the surface and where the air is dry , so that a high evaporation leaves salty deposits which permit only sparse plant growth . 
Meaning of the word marked with <WSD> tags:  binary compound that occurs at room temperature as a clear colorless odorless tasteless liquid; freezes into ice below 0 degrees centigrade and boils above 100 degrees centigrade; widely used as a solvent