The cost savings for the hotel is not just water and detergent, it's also labor. I would guess that labor is the biggest expense, given that the sheets and towels aren't just washed, the maid folds them and makes the bed as well. This has nothing to do with the environment, and I feel insulted when I see those placards in a hotel room. If I'm in a hotel, it means I'm on vacation, which means I insist the sheets and towels be changed every day. If I got a discount on the room rate then it would be a different story but we know that isn't the case.