expression, godan verb (-ru)
A common expression for giving water to plants, flowers, or crops. The verb やる here means 'to give' in a casual, often nurturing sense.
毎朝、庭の花に水をやる。
I water the garden flowers every morning.
鉢植えの土が乾いたら、水をやって
When the soil of the potted plant dries out, please water it.