a water-saving device的用法和样例：
- Planting under a film, a new planting technique, is combined with drip irrigation, a water saving irrigation technique, to form a new method of developing and utilizing saline-alkali soil.
- a Water Saving and Pollution Prevention Society
- A water power station must have a dam.
- Every apartment house has a water tank on its roof.
- The police used a water cannon on the rioters and soon brought them to heel.