Choose the correct word to fill each blank in the following passage

Our future house will be on the ocean. It will be surrounded by tall trees and blue sea but we only have salt water in the ocean. We need fresh water for (26) .......... (drink/ drinking/ to drink/ to drinking) and for growing food (27) ......... (in/ on/ at/ into) farms.

Ocean water is too salty (28) ......... (drink/ drinking/ to drink/ to drinking). It is also too salty for watering plants. We must have the (29) .......... (things/ suggestions/ ways/ ideas) to make fresh water from salty water. We should be (30) .......... (careful/ careless/ carefully/ carelessly) not to waste water.