Sentence:  study methods for the recovery and marketing of commercially valuable byproducts resulting from the conversion of saline water ; and undertake economic studies and surveys to determine present and prospective costs of producing water for beneficial consumptive <WSD>purposes</WSD> in various parts of the United States by the leading saline water processes as compared with other standard methods . 
Meaning of the word marked with <WSD> tags:  what something is used for