expression, godan verb (-su)
fill with water
Used for filling a container, such as a glass, with water. The object is marked with を.
コップに水を満たしてください。
Please fill the glass with water.
花瓶に水を満たしてから花を生けた。
I filled the vase with water and then arranged the flowers.
満たす is a general verb meaning 'to fill' or 'to satisfy'. 水を満たす is a specific expression using 満たす with water as the object.
Phrase composed of 水 (water) + を (object marker) + 満たす (to fill).