This is the 9483rd most frequent Japanese word.
節水
Water conservation.
節水 in this sentence is used as a noun expanded to mean water conservation, representing the concept of saving water.
私たちは節水に努めるべきです。
We should strive to conserve water.
節水 here modifies 機能 to describe a feature related to water saving. It acts as an adjective in this context.
新しいシャワーは節水機能が付いています。
The new shower has a water-saving feature.
節水 is used to describe the purpose or reason, indicating the action taken for water saving.