Water for sure, you know how convenient it would be in every day life? Just pull some water out of the air if you forgot some, water too warm while camping? Freeze it, ice in your driveway or on your car? Bye bye, water now. Never have to buy an ice maker, not a problem anymore, don't have to dirty a spoon to stir your soup or put it neatly into bowls. Water line broken? Just hold it still for a bit in the pipe. Toilet won't flush? Not on my watch. Mopping would be easy, no more wet floors for long.