Sentence:  Greasy soils are hardly removed by washing in plain <WSD>water</WSD> ; and natural waters , in addition , often contain impurities such as calcium salts which can react with soils to make them more difficult to remove . 
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